Allow spells and entities to retain their owner if the owner is offline (multiplayer) or in another dimension (nether), and handle situations where the owner is not around (getOwner() == null)

src/main/java/com/minelittlepony/unicopia/Owned.java

@@ -1,19 +1,55 @@
 package com.minelittlepony.unicopia;
 
+import java.util.Optional;
+import java.util.UUID;
+
+import org.jetbrains.annotations.Nullable;
+
+import net.minecraft.entity.Entity;
+
 /**
- * Interface for things that can be owned.
+ * Interface for things that can be owned by an entity.
+ * <p>
+ * Ownership is retained so long as the owner is still active. If the owner leaves or dies, the link is broken.
  *
  * @param <E> The type of object that owns us.
  */
-public interface Owned<E> {
+public interface Owned<E extends Entity> {
+    /**
+     * Gets the owner that holds this object.
+     */
+    @Nullable
+    E getMaster();
+
+    /**
+     * Gets the unique entity id of the entity that holds this object.
+     * <p>
+     * Since {@link Owned#getMaster()} will only return if the owner is loaded, use this to perform checks
+     * in the owner's absence.
+     */
+    default Optional<UUID> getMasterId() {
+        return Optional.of(getMaster()).map(Entity::getUuid);
+    }
 
     /**
      * Updates the owner of this object.
      */
-    void setMaster(E owner);
+    void setMaster(@Nullable E owner);
 
     /**
-     * Gets the owner that holds this object.
+     * Updated the owner of this object to be the same as another.
+     *
+     * @param sibling
      */
-    E getMaster();
+    default void setMaster(Owned<? extends E> sibling) {
+        setMaster(sibling.getMaster());
+    }
+
+    default boolean isOwnedBy(@Nullable Object owner) {
+        return owner instanceof Entity e && getMasterId().isPresent() && e.getUuid().equals(getMasterId().get());
+    }
+
+    default boolean hasCommonOwner(Owned<?> sibling) {
+        return getMasterId().isPresent() && getMasterId().equals(sibling.getMasterId());
+    }
 }

src/main/java/com/minelittlepony/unicopia/WeaklyOwned.java

@@ -0,0 +1,54 @@
+package com.minelittlepony.unicopia;
+
+import java.util.Optional;
+import java.util.UUID;
+
+import org.jetbrains.annotations.Nullable;
+
+import com.minelittlepony.unicopia.entity.EntityReference;
+
+import net.minecraft.entity.Entity;
+import net.minecraft.world.World;
+
+/**
+ * Interface for things that can be weakly owned (by an entity).
+ * Ownership links for these kinds of owned instances are preserved even if the owner is not present to oversee it.
+ *
+ * @param <E> The type of object that owns us.
+ */
+public interface WeaklyOwned<E extends Entity> extends Owned<E> {
+
+    World getWorld();
+
+    EntityReference<E> getMasterReference();
+
+    /**
+     * Updated the owner of this object to be the same as another.
+     *
+     * @param sibling
+     */
+    @SuppressWarnings("unchecked")
+    default void setMaster(WeaklyOwned<? extends E> sibling) {
+        if (sibling instanceof WeaklyOwned) {
+            getMasterReference().copyFrom(((WeaklyOwned<E>)sibling).getMasterReference());
+        } else {
+            setMaster(sibling.getMaster());
+        }
+    }
+
+    @Nullable
+    @Override
+    default E getMaster() {
+        return getMasterReference().get(getWorld());
+    }
+
+    @Override
+    default void setMaster(E master) {
+        getMasterReference().set(master);
+    }
+
+    @Override
+    default Optional<UUID> getMasterId() {
+        return getMasterReference().getId();
+    }
+}

src/main/java/com/minelittlepony/unicopia/ability/UnicornDispellAbility.java

@@ -62,7 +62,7 @@ public class UnicornDispellAbility implements Ability<Pos> {
     @Override
     public double getCostEstimate(Pony player) {
         return getTarget(player)
-                .filter(caster -> caster.getMaster() != player.getMaster())
+                .filter(caster -> !caster.hasCommonOwner(player))
                 .isPresent() ? 10 : 0;
     }
 

src/main/java/com/minelittlepony/unicopia/ability/UnicornTeleportAbility.java

@@ -129,12 +129,17 @@ public class UnicornTeleportAbility implements Ability<Pos> {
     }
 
     protected void teleport(Pony teleporter, Caster<?> teleportee, Pos destination) {
+
+        LivingEntity player = teleportee.getMaster();
+
+        if (player == null) {
+            return;
+        }
+
         teleportee.getWorld().playSound(null, teleportee.getOrigin(), SoundEvents.ENTITY_ITEM_PICKUP, SoundCategory.PLAYERS, 1, 1);
 
         double distance = destination.distanceTo(teleportee) / 10;
 
-        LivingEntity player = teleportee.getMaster();
-
         if (player.hasVehicle()) {
             Entity mount = player.getVehicle();
 

src/main/java/com/minelittlepony/unicopia/ability/magic/spell/PlaceableSpell.java

@@ -2,6 +2,7 @@ package com.minelittlepony.unicopia.ability.magic.spell;
 
 import java.util.Collection;
 import java.util.List;
+import java.util.Optional;
 
 import org.jetbrains.annotations.Nullable;
 
@@ -18,6 +19,9 @@ import com.minelittlepony.unicopia.particle.UParticles;
 import net.minecraft.nbt.NbtCompound;
 import net.minecraft.util.Identifier;
 import net.minecraft.util.math.Vec3d;
+import net.minecraft.util.registry.Registry;
+import net.minecraft.util.registry.RegistryKey;
+import net.minecraft.world.World;
 
 /**
  * A spell that can be attached to a specific location in the world.
@@ -26,13 +30,25 @@ import net.minecraft.util.math.Vec3d;
  * spell loses affect until they return.
  */
 public class PlaceableSpell extends AbstractDelegatingSpell {
+    /**
+     * Dimension the spell was originally cast in
+     */
     @Nullable
-    private Identifier dimension;
+    private RegistryKey<World> dimension;
 
+    /**
+     * The visual effect
+     */
     private final ParticleHandle particlEffect = new ParticleHandle();
 
+    /**
+     * The cast spell entity
+     */
     private final EntityReference<CastSpellEntity> castEntity = new EntityReference<>();
 
+    /**
+     * The spell being cast
+     */
     private Spell spell;
 
     public PlaceableSpell(SpellType<?> type, SpellTraits traits) {
@@ -59,19 +75,18 @@ public class PlaceableSpell extends AbstractDelegatingSpell {
     public boolean tick(Caster<?> source, Situation situation) {
         if (situation == Situation.BODY) {
             if (!source.isClient()) {
+
                 if (dimension == null) {
-                    dimension = source.getWorld().getRegistryKey().getValue();
+                    dimension = source.getWorld().getRegistryKey();
                     setDirty();
-                } else if (!source.getWorld().getRegistryKey().getValue().equals(dimension)) {
-                    return false;
                 }
 
-                if (!castEntity.isPresent(source.getWorld())) {
+                if (getSpellEntity(source).isEmpty()) {
                     CastSpellEntity entity = UEntities.CAST_SPELL.create(source.getWorld());
                     Vec3d pos = castEntity.getPosition().orElse(source.getOriginVector());
                     entity.updatePositionAndAngles(pos.x, pos.y, pos.z, 0, 0);
                     entity.getSpellSlot().put(this);
-                    entity.setMaster(source.getMaster());
+                    entity.setMaster(source);
                     entity.world.spawnEntity(entity);
 
                     castEntity.set(entity);
@@ -92,14 +107,33 @@ public class PlaceableSpell extends AbstractDelegatingSpell {
             return super.tick(source, Situation.GROUND);
         }
 
+        this.onDestroyed(source);
+
         return !isDead();
     }
 
+    @Override
+    public void onDestroyed(Caster<?> source) {
+        if (!source.isClient()) {
+            getSpellEntity(source).ifPresent(e -> {
+                e.getSpellSlot().clear();
+                castEntity.set(null);
+            });
+        }
+        super.onDestroyed(source);
+    }
+
+    protected Optional<CastSpellEntity> getSpellEntity(Caster<?> source) {
+        return Optional.ofNullable(dimension)
+                .map(dim -> source.getWorld().getServer().getWorld(dimension))
+                .map(castEntity::get);
+    }
+
     @Override
     public void toNBT(NbtCompound compound) {
         super.toNBT(compound);
         if (dimension != null) {
-            compound.putString("dimension", dimension.toString());
+            compound.putString("dimension", dimension.getValue().toString());
         }
         compound.put("castEntity", castEntity.toNBT());
         compound.put("spell", Spell.writeNbt(spell));
@@ -109,7 +143,10 @@ public class PlaceableSpell extends AbstractDelegatingSpell {
     public void fromNBT(NbtCompound compound) {
         super.fromNBT(compound);
         if (compound.contains("dimension")) {
-            dimension = new Identifier(compound.getString("dimension"));
+            Identifier id = Identifier.tryParse(compound.getString("dimension"));
+            if (id != null) {
+                dimension = RegistryKey.of(Registry.WORLD_KEY, id);
+            }
         }
         if (compound.contains("castEntity")) {
             castEntity.fromNBT(compound.getCompound("castEntity"));

src/main/java/com/minelittlepony/unicopia/ability/magic/spell/RainboomAbilitySpell.java

@@ -62,6 +62,10 @@ public class RainboomAbilitySpell extends AbstractSpell {
 
         LivingEntity owner = source.getMaster();
 
+        if (owner == null) {
+            return false;
+        }
+
         source.findAllEntitiesInRange(rad).forEach(e -> {
             e.damage(MagicalDamageSource.create("rainboom", source), 6);
         });

src/main/java/com/minelittlepony/unicopia/ability/magic/spell/ThrowableSpell.java

@@ -53,6 +53,10 @@ public final class ThrowableSpell extends AbstractDelegatingSpell {
 
         LivingEntity entity = caster.getMaster();
 
+        if (entity == null) {
+            return Optional.empty();
+        }
+
         caster.playSound(SoundEvents.ITEM_CHORUS_FRUIT_TELEPORT, 0.7F, 0.4F / (world.random.nextFloat() * 0.4F + 0.8F));
 
         if (!caster.isClient()) {

src/main/java/com/minelittlepony/unicopia/ability/magic/spell/effect/CatapultSpell.java

@@ -86,7 +86,7 @@ public class CatapultSpell extends AbstractSpell implements ProjectileSpell {
 
         double maxDistance = 2 + (getTraits().get(Trait.FOCUS) - 50) * 8;
 
-        HitResult ray = RayTraceHelper.doTrace(caster.getMaster(), maxDistance, 1, EntityPredicates.CAN_COLLIDE).getResult();
+        HitResult ray = RayTraceHelper.doTrace(caster.getEntity(), maxDistance, 1, EntityPredicates.CAN_COLLIDE).getResult();
 
         if (ray.getType() == HitResult.Type.ENTITY) {
             EntityHitResult result = (EntityHitResult)ray;

src/main/java/com/minelittlepony/unicopia/ability/magic/spell/effect/DarkVortexSpell.java

@@ -1,5 +1,7 @@
 package com.minelittlepony.unicopia.ability.magic.spell.effect;
 
+import org.jetbrains.annotations.Nullable;
+
 import com.minelittlepony.unicopia.ability.magic.Affine;
 import com.minelittlepony.unicopia.ability.magic.Caster;
 import com.minelittlepony.unicopia.ability.magic.spell.Situation;
@@ -198,13 +200,18 @@ public class DarkVortexSpell extends AttractiveSpell {
         if (distance <= getEventHorizonRadius()) {
             target.setVelocity(target.getVelocity().multiply(distance / (2 * radius)));
 
+            @Nullable
+            Entity master = source.getMaster();
+
             if (target instanceof MagicProjectileEntity) {
                 Item item = ((MagicProjectileEntity)target).getStack().getItem();
-                if (item instanceof ProjectileDelegate) {
-                    ((ProjectileDelegate) item).onImpact(((MagicProjectileEntity)target), source.getMaster());
+                if (item instanceof ProjectileDelegate && master != null) {
+                    ((ProjectileDelegate) item).onImpact(((MagicProjectileEntity)target), master);
                 }
             } else if (target instanceof PersistentProjectileEntity) {
-                source.getMaster().damage(DamageSource.thrownProjectile(target, ((PersistentProjectileEntity)target).getOwner()), 4);
+                if (master != null) {
+                    master.damage(DamageSource.thrownProjectile(target, ((PersistentProjectileEntity)target).getOwner()), 4);
+                }
                 target.discard();
                 return;
             }

src/main/java/com/minelittlepony/unicopia/ability/magic/spell/effect/FeatherFallSpell.java

@@ -58,13 +58,12 @@ public class FeatherFallSpell extends AbstractSpell {
         final float strength = 1F / (getTraits().get(Trait.STRENGTH, 2, 9) / targets.size());
         final float generosity = getTraits().get(Trait.GENEROSITY, 1, MAX_GENEROSITY_FACTOR) / MAX_GENEROSITY_FACTOR;
 
-        Entity master = caster.getMaster();
         Entity entity = caster.getEntity();
         Vec3d masterVelocity = caster.getEntity().getVelocity().multiply(0.1);
         targets.forEach(target -> {
             if (target.getVelocity().y < 0) {
 
-                boolean isSelf = target == master || target == entity;
+                boolean isSelf = caster.isOwnedBy(target) || target == entity;
                 float delta = strength * (isSelf ? (1F - generosity) : generosity);
 
                 if (!isSelf || generosity < 0.5F) {

src/main/java/com/minelittlepony/unicopia/ability/magic/spell/effect/FireSpell.java

@@ -1,5 +1,7 @@
 package com.minelittlepony.unicopia.ability.magic.spell.effect;
 
+import org.jetbrains.annotations.Nullable;
+
 import com.minelittlepony.unicopia.EquinePredicates;
 import com.minelittlepony.unicopia.ability.magic.Caster;
 import com.minelittlepony.unicopia.ability.magic.spell.Situation;
@@ -48,7 +50,7 @@ public class FireSpell extends AbstractAreaEffectSpell implements ProjectileSpel
     @Override
     public void onImpact(MagicProjectileEntity projectile, BlockPos pos, BlockState state) {
         if (!projectile.isClient()) {
-            projectile.getWorld().createExplosion(projectile.getMaster(), pos.getX(), pos.getY(), pos.getZ(), 2, DestructionType.DESTROY);
+            projectile.getWorld().createExplosion(projectile.getEntity(), pos.getX(), pos.getY(), pos.getZ(), 2, DestructionType.DESTROY);
         }
     }
 
@@ -112,11 +114,11 @@ public class FireSpell extends AbstractAreaEffectSpell implements ProjectileSpel
         return false;
     }
 
-    protected boolean applyEntities(Entity owner, World world, Vec3d pos) {
+    protected boolean applyEntities(@Nullable Entity owner, World world, Vec3d pos) {
         return !VecHelper.findInRange(owner, world, pos, Math.max(0, 3 + getTraits().get(Trait.POWER)), i -> applyEntitySingle(owner, world, i)).isEmpty();
     }
 
-    protected boolean applyEntitySingle(Entity owner, World world, Entity e) {
+    protected boolean applyEntitySingle(@Nullable Entity owner, World world, Entity e) {
         if ((!e.equals(owner) ||
                 (owner instanceof PlayerEntity && !EquinePredicates.PLAYER_UNICORN.test(owner))) && !(e instanceof ItemEntity)
         && !(e instanceof Caster<?>)) {
@@ -129,7 +131,7 @@ public class FireSpell extends AbstractAreaEffectSpell implements ProjectileSpel
         return false;
     }
 
-    protected DamageSource getDamageCause(Entity target, LivingEntity attacker) {
+    protected DamageSource getDamageCause(Entity target, @Nullable LivingEntity attacker) {
         return MagicalDamageSource.create("fire", attacker);
     }
 

src/main/java/com/minelittlepony/unicopia/ability/magic/spell/effect/IceSpell.java

@@ -43,12 +43,10 @@ public class IceSpell extends AbstractSpell {
 
     @Override
     public boolean tick(Caster<?> source, Situation situation) {
-        LivingEntity owner = source.getMaster();
-
         boolean submerged = source.getEntity().isSubmergedInWater() || source.getEntity().isSubmergedIn(FluidTags.LAVA);
 
         long blocksAffected = PosHelper.getAllInRegionMutable(source.getOrigin(), outerRange).filter(i -> {
-            if (source.canModifyAt(i) && applyBlockSingle(owner, source.getWorld(), i, situation)) {
+            if (source.canModifyAt(i) && applyBlockSingle(source.getEntity(), source.getWorld(), i, situation)) {
 
                 if (submerged & source.getOrigin().isWithinDistance(i, rad - 1)) {
                     BlockState state = source.getWorld().getBlockState(i);

src/main/java/com/minelittlepony/unicopia/ability/magic/spell/effect/LightSpell.java

@@ -59,9 +59,9 @@ public class LightSpell extends AbstractSpell {
                 if (!ref.isPresent(caster.getWorld())) {
                     FairyEntity entity = UEntities.TWITTERMITE.create(caster.getWorld());
                     entity.setPosition(ref.getPosition().orElseGet(() -> {
-                        return caster.getMaster().getPos().add(VecHelper.supply(() -> caster.getWorld().random.nextInt(3) - 1));
+                        return caster.getOriginVector().add(VecHelper.supply(() -> caster.getWorld().random.nextInt(3) - 1));
                     }));
-                    entity.setMaster(caster.getMaster());
+                    entity.setMaster(caster);
                     entity.world.spawnEntity(entity);
 
                     ref.set(entity);

src/main/java/com/minelittlepony/unicopia/ability/magic/spell/effect/NecromancySpell.java

@@ -139,7 +139,7 @@ public class NecromancySpell extends AbstractAreaEffectSpell {
         minion.equipStack(EquipmentSlot.HEAD, Items.IRON_HELMET.getDefaultStack());
 
         Equine.of(minion).filter(eq -> eq instanceof Creature).ifPresent(eq -> {
-            ((Creature)eq).setMaster(source.getMaster());
+            ((Creature)eq).setMaster(source);
         });
 
         source.getWorld().spawnEntity(minion);

src/main/java/com/minelittlepony/unicopia/ability/magic/spell/effect/ShieldSpell.java

@@ -109,7 +109,7 @@ public class ShieldSpell extends AbstractSpell {
      * Calculates the maximum radius of the shield. aka The area of effect.
      */
     public double getDrawDropOffRange(Caster<?> source) {
-        float multiplier = source.getMaster().isSneaking() ? 1 : 2;
+        float multiplier = source.getMaster() != null && source.getMaster().isSneaking() ? 1 : 2;
         float min = 4 + getTraits().get(Trait.POWER);
         return (min + (source.getLevel().get() * 2)) / multiplier;
     }

src/main/java/com/minelittlepony/unicopia/ability/magic/spell/effect/SiphoningSpell.java

@@ -109,7 +109,7 @@ public class SiphoningSpell extends AbstractAreaEffectSpell {
 
     private void collectHealth(Caster<?> source) {
         LivingEntity owner = source.getMaster();
-        float maxHealthGain = owner.getMaxHealth() - owner.getHealth();
+        float maxHealthGain = owner == null ? 0 : owner.getMaxHealth() - owner.getHealth();
 
         if (maxHealthGain == 0) {
             return;

src/main/java/com/minelittlepony/unicopia/ability/magic/spell/effect/TargetSelecter.java

@@ -29,22 +29,10 @@ public class TargetSelecter {
     public Stream<Entity> getEntities(Caster<?> source, double radius, BiPredicate<Caster<?>, Entity> filter) {
         targets.values().removeIf(Target::tick);
 
-        Entity owner = source.getMaster();
-
-        boolean ownerIsValid = spell.isFriendlyTogether(source) && (EquinePredicates.PLAYER_UNICORN.test(owner));
+        Predicate<Entity> ownerCheck = isOwnerOrFriend(spell, source);
 
         return source.findAllEntitiesInRange(radius)
-            .filter(entity -> entity.isAlive() && !entity.isRemoved())
-            .filter(entity -> {
-                boolean hasShield = SpellPredicate.IS_SHIELD_LIKE.isOn(entity);
-                boolean isOwnerOrFriend = Pony.equal(entity, owner) || owner.isConnectedThroughVehicle(entity) || FriendshipBraceletItem.isComrade(source, entity);
-
-                if (!ownerIsValid && isOwnerOrFriend) {
-                    return true;
-                }
-
-                return !hasShield && (!ownerIsValid || !isOwnerOrFriend);
-            })
+            .filter(entity -> entity.isAlive() && !entity.isRemoved() && !ownerCheck.test(entity) && !SpellPredicate.IS_SHIELD_LIKE.isOn(entity))
             .filter(e -> filter.test(source, e))
             .map(i -> {
                 targets.computeIfAbsent(i.getUuid(), Target::new);
@@ -57,16 +45,18 @@ public class TargetSelecter {
     }
 
     public static <T extends Entity> Predicate<T> notOwnerOrFriend(Affine spell, Caster<?> source) {
+        return TargetSelecter.<T>isOwnerOrFriend(spell, source).negate();
+    }
+
+    public static <T extends Entity> Predicate<T> isOwnerOrFriend(Affine spell, Caster<?> source) {
         Entity owner = source.getMaster();
 
-        boolean ownerIsValid = spell.isFriendlyTogether(source) && (EquinePredicates.PLAYER_UNICORN.test(owner));
-
-        if (!ownerIsValid) {
-            return e -> true;
+        if (!(spell.isFriendlyTogether(source) && EquinePredicates.PLAYER_UNICORN.test(owner))) {
+            return e -> FriendshipBraceletItem.isComrade(source, e);
         }
 
         return entity -> {
-            return !ownerIsValid || !(Pony.equal(entity, owner) || owner.isConnectedThroughVehicle(entity) || FriendshipBraceletItem.isComrade(source, entity));
+            return FriendshipBraceletItem.isComrade(source, entity) || (owner != null && (Pony.equal(entity, owner) || owner.isConnectedThroughVehicle(entity)));
         };
     }
 

src/main/java/com/minelittlepony/unicopia/entity/CastSpellEntity.java

@@ -1,9 +1,7 @@
 package com.minelittlepony.unicopia.entity;
 
-import java.util.Optional;
-import java.util.UUID;
-
 import com.minelittlepony.unicopia.Affinity;
+import com.minelittlepony.unicopia.WeaklyOwned;
 import com.minelittlepony.unicopia.ability.magic.Caster;
 import com.minelittlepony.unicopia.ability.magic.Levelled;
 import com.minelittlepony.unicopia.ability.magic.SpellContainer;
@@ -12,6 +10,7 @@ import com.minelittlepony.unicopia.ability.magic.spell.Situation;
 import com.minelittlepony.unicopia.ability.magic.spell.Spell;
 import com.minelittlepony.unicopia.network.Channel;
 import com.minelittlepony.unicopia.network.MsgSpawnProjectile;
+import com.minelittlepony.unicopia.network.datasync.EffectSync;
 
 import net.minecraft.entity.Entity;
 import net.minecraft.entity.EntityType;
@@ -25,45 +24,25 @@ import net.minecraft.text.Text;
 import net.minecraft.text.TranslatableText;
 import net.minecraft.world.World;
 
-public class CastSpellEntity extends LightEmittingEntity implements Caster<LivingEntity> {
+public class CastSpellEntity extends LightEmittingEntity implements Caster<LivingEntity>, WeaklyOwned<LivingEntity> {
     private static final TrackedData<Float> GRAVITY = DataTracker.registerData(CastSpellEntity.class, TrackedDataHandlerRegistry.FLOAT);
-    private static final TrackedData<Optional<UUID>> SPELL = DataTracker.registerData(CastSpellEntity.class, TrackedDataHandlerRegistry.OPTIONAL_UUID);
+    private static final TrackedData<NbtCompound> EFFECT = DataTracker.registerData(CastSpellEntity.class, TrackedDataHandlerRegistry.TAG_COMPOUND);
 
     private static final LevelStore LEVELS = Levelled.fixed(0);
 
     private final EntityPhysics<CastSpellEntity> physics = new EntityPhysics<>(this, GRAVITY);
 
-    private final SpellContainer spell = new SpellContainer.Delegate() {
-        @Override
-        public SpellContainer delegate() {
-            return Caster.of(getMaster()).map(Caster::getSpellSlot).orElse(SpellContainer.EMPTY);
-        }
-
-        @Override
-        public void put(Spell spell) {
-            getDataTracker().set(SPELL, Optional.ofNullable(spell).map(Spell::getUuid));
-            SpellContainer.Delegate.super.put(spell);
-        }
-
-        @Override
-        public boolean clear() {
-            return getDataTracker().get(SPELL).map(id -> {
-                return delegate().removeIf(spell -> spell.getUuid().equals(id), true);
-            }).orElse(false);
-        }
-    };
+    private final EffectSync effectDelegate = new EffectSync(this, EFFECT);
 
     private final EntityReference<LivingEntity> owner = new EntityReference<>();
 
-    private int orphanedTicks;
-
     public CastSpellEntity(EntityType<?> type, World world) {
         super(type, world);
     }
 
     @Override
     protected void initDataTracker() {
-        getDataTracker().startTracking(SPELL, Optional.empty());
+        getDataTracker().startTracking(EFFECT, new NbtCompound());
     }
 
     @Override
@@ -88,35 +67,14 @@ public class CastSpellEntity extends LightEmittingEntity implements Caster<Livin
             return;
         }
 
-        LivingEntity master = getMaster();
-
-        if (master == null || master.isRemoved()) {
-            if (orphanedTicks-- > 0) {
-                return;
-            }
-            discard();
-            return;
-        }
-
-        orphanedTicks = 0;
-
-        if (dataTracker.get(SPELL).filter(spellId -> {
-            return getSpellSlot().forEach(spell -> {
-                return spell.getUuid().equals(spellId) ? Operation.ofBoolean(spell.tick(this, Situation.GROUND_ENTITY)) : Operation.SKIP;
-            }, true);
-        }).isEmpty()) {
+        if (!getSpellSlot().forEach(spell -> Operation.ofBoolean(spell.tick(this, Situation.GROUND_ENTITY)), true)) {
             discard();
         }
     }
 
     @Override
-    public void setMaster(LivingEntity owner) {
-        this.owner.set(owner);
-    }
-
-    @Override
-    public LivingEntity getMaster() {
-        return owner.get(((Entity)this).world);
+    public EntityReference<LivingEntity> getMasterReference() {
+        return owner;
     }
 
     @Override
@@ -141,7 +99,7 @@ public class CastSpellEntity extends LightEmittingEntity implements Caster<Livin
 
     @Override
     public SpellContainer getSpellSlot() {
-        return spell;
+        return effectDelegate;
     }
 
     @Override
@@ -152,8 +110,8 @@ public class CastSpellEntity extends LightEmittingEntity implements Caster<Livin
     @Override
     protected void writeCustomDataToNbt(NbtCompound tag) {
         tag.put("owner", owner.toNBT());
-        dataTracker.get(SPELL).ifPresent(spellId -> {
-            tag.putUuid("spellId", spellId);
+        getSpellSlot().get(true).ifPresent(effect -> {
+            tag.put("effect", Spell.writeNbt(effect));
         });
     }
 
@@ -162,9 +120,8 @@ public class CastSpellEntity extends LightEmittingEntity implements Caster<Livin
         if (tag.contains("owner")) {
             owner.fromNBT(tag.getCompound("owner"));
         }
-        orphanedTicks = 60;
-        if (tag.contains("spellId")) {
-            dataTracker.set(SPELL, Optional.ofNullable(tag.getUuid("spellId")));
+        if (tag.contains("effect")) {
+            getSpellSlot().put(Spell.readNbt(tag.getCompound("effect")));
         }
     }
 

src/main/java/com/minelittlepony/unicopia/entity/Creature.java

@@ -3,10 +3,12 @@ package com.minelittlepony.unicopia.entity;
 import java.util.Optional;
 import java.util.function.Predicate;
 
+import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
 import com.minelittlepony.unicopia.Affinity;
 import com.minelittlepony.unicopia.Race;
+import com.minelittlepony.unicopia.WeaklyOwned;
 import com.minelittlepony.unicopia.ability.magic.Affine;
 import com.minelittlepony.unicopia.ability.magic.Levelled;
 import com.minelittlepony.unicopia.ability.magic.spell.Spell;
@@ -33,8 +35,9 @@ import net.minecraft.entity.mob.SlimeEntity;
 import net.minecraft.entity.player.PlayerEntity;
 import net.minecraft.nbt.NbtCompound;
 import net.minecraft.nbt.NbtElement;
+import net.minecraft.world.World;
 
-public class Creature extends Living<LivingEntity> {
+public class Creature extends Living<LivingEntity> implements WeaklyOwned<LivingEntity> {
     private static final TrackedData<NbtCompound> EFFECT = DataTracker.registerData(LivingEntity.class, TrackedDataHandlerRegistry.TAG_COMPOUND);
     private static final TrackedData<NbtCompound> MASTER = DataTracker.registerData(LivingEntity.class, TrackedDataHandlerRegistry.TAG_COMPOUND);
     public static final TrackedData<Float> GRAVITY = DataTracker.registerData(LivingEntity.class, TrackedDataHandlerRegistry.FLOAT);
@@ -68,17 +71,27 @@ public class Creature extends Living<LivingEntity> {
     }
 
     public boolean isMinion() {
-        Entity master = getMaster();
-        return master != null && master != getEntity();
+        return master.getId().isPresent();
     }
 
     @Override
+    public World getWorld() {
+        return super.getWorld();
+    }
+
+    @Override
+    @NotNull
     public LivingEntity getMaster() {
         NbtCompound data = entity.getDataTracker().get(MASTER);
         master.fromNBT(data);
         return master.getOrEmpty(getWorld()).orElse(entity);
     }
 
+    @Override
+    public EntityReference<LivingEntity> getMasterReference() {
+        return master;
+    }
+
     @Override
     public Entity getEntity() {
         return entity;
@@ -112,7 +125,7 @@ public class Creature extends Living<LivingEntity> {
         Predicate<LivingEntity> filter = TargetSelecter.<LivingEntity>notOwnerOrFriend(this, this).and(e -> {
             return Equine.of(e)
                     .filter(eq -> eq instanceof Creature)
-                    .filter(eq -> ((Creature)eq).getMaster() == getMaster())
+                    .filter(eq -> ((Creature)eq).hasCommonOwner(this))
                     .isEmpty();
         });
 

src/main/java/com/minelittlepony/unicopia/entity/EntityReference.java

@@ -17,7 +17,7 @@ import net.minecraft.world.World;
 
 public class EntityReference<T extends Entity> implements NbtSerialisable {
 
-    private UUID uuid;
+    private Optional<UUID> uuid = Optional.empty();
     private int clientId;
 
     private Optional<Vec3d> pos = Optional.empty();
@@ -32,18 +32,28 @@ public class EntityReference<T extends Entity> implements NbtSerialisable {
         fromNBT(nbt);
     }
 
+    public void copyFrom(EntityReference<T> other) {
+        uuid = other.uuid;
+        clientId = other.clientId;
+        pos = other.pos;
+    }
+
     public void set(@Nullable T entity) {
         if (entity != null) {
-            uuid = entity.getUuid();
+            uuid = Optional.of(entity.getUuid());
             clientId = entity.getId();
             pos = Optional.of(entity.getPos());
         } else {
-            uuid = null;
+            uuid = Optional.empty();
             clientId = 0;
             pos = Optional.empty();
         }
     }
 
+    public Optional<UUID> getId() {
+        return uuid;
+    }
+
     /**
      * Gets the position the last known position of the assigned entity.
      */
@@ -66,8 +76,8 @@ public class EntityReference<T extends Entity> implements NbtSerialisable {
 
     @SuppressWarnings("unchecked")
     public Optional<T> getOrEmpty(World world) {
-        if (uuid != null && world instanceof ServerWorld) {
-            return Optional.ofNullable((T)((ServerWorld)world).getEntity(uuid)).filter(this::checkReference);
+        if (uuid.isPresent() && world instanceof ServerWorld) {
+            return uuid.map(((ServerWorld)world)::getEntity).map(e -> (T)e).filter(this::checkReference);
         }
 
         if (clientId != 0) {
@@ -84,18 +94,14 @@ public class EntityReference<T extends Entity> implements NbtSerialisable {
 
     @Override
     public void toNBT(NbtCompound tag) {
-        if (uuid != null) {
-            tag.putUuid("uuid", uuid);
-        }
-        pos.ifPresent(p -> {
-            tag.put("pos", NbtSerialisable.writeVector(p));
-        });
+        uuid.ifPresent(uuid -> tag.putUuid("uuid", uuid));
+        pos.ifPresent(p -> tag.put("pos", NbtSerialisable.writeVector(p)));
         tag.putInt("clientId", clientId);
     }
 
     @Override
     public void fromNBT(NbtCompound tag) {
-        uuid = tag.containsUuid("uuid") ? tag.getUuid("uuid") : null;
+        uuid = tag.containsUuid("uuid") ? Optional.of(tag.getUuid("uuid")) : Optional.empty();
         pos = tag.contains("pos") ? Optional.ofNullable(NbtSerialisable.readVector(tag.getList("pos", NbtElement.DOUBLE_TYPE))) : Optional.empty();
         clientId = tag.getInt("clientId");
     }

src/main/java/com/minelittlepony/unicopia/entity/FairyEntity.java

@@ -5,8 +5,8 @@ import java.util.Optional;
 
 import org.jetbrains.annotations.Nullable;
 
-import com.minelittlepony.unicopia.Owned;
 import com.minelittlepony.unicopia.USounds;
+import com.minelittlepony.unicopia.WeaklyOwned;
 import com.minelittlepony.unicopia.particle.MagicParticleEffect;
 import com.minelittlepony.unicopia.particle.ParticleUtils;
 import com.minelittlepony.unicopia.particle.UParticles;
@@ -42,7 +42,7 @@ import net.minecraft.util.math.Vec3d;
 import net.minecraft.world.World;
 import net.minecraft.world.event.GameEvent;
 
-public class FairyEntity extends PathAwareEntity implements DynamicLightSource, Owned<LivingEntity> {
+public class FairyEntity extends PathAwareEntity implements DynamicLightSource, WeaklyOwned<LivingEntity> {
     private final EntityReference<LivingEntity> owner = new EntityReference<>();
 
     private final EntityReference<LivingEntity> assignment = new EntityReference<>();
@@ -101,13 +101,8 @@ public class FairyEntity extends PathAwareEntity implements DynamicLightSource,
     }
 
     @Override
-    public void setMaster(LivingEntity owner) {
-        this.owner.set(owner);
-    }
-
-    @Override
-    public LivingEntity getMaster() {
-        return owner.get(((Entity)this).world);
+    public EntityReference<LivingEntity> getMasterReference() {
+        return owner;
     }
 
     @Override

src/main/java/com/minelittlepony/unicopia/entity/ItemImpl.java

@@ -2,6 +2,8 @@ package com.minelittlepony.unicopia.entity;
 
 import java.util.Random;
 
+import org.jetbrains.annotations.NotNull;
+
 import com.minelittlepony.unicopia.Owned;
 import com.minelittlepony.unicopia.Race;
 import com.minelittlepony.unicopia.UTags;
@@ -132,12 +134,12 @@ public class ItemImpl implements Equine<ItemEntity>, Owned<ItemEntity> {
 
     @Override
     public Race getSpecies() {
-        return Race.fromId(getMaster().getDataTracker().get(ITEM_RACE));
+        return Race.fromId(owner.getDataTracker().get(ITEM_RACE));
     }
 
     @Override
     public void setSpecies(Race race) {
-        getMaster().getDataTracker().set(ITEM_RACE, race.ordinal());
+        owner.getDataTracker().set(ITEM_RACE, race.ordinal());
     }
 
     @Override
@@ -158,6 +160,7 @@ public class ItemImpl implements Equine<ItemEntity>, Owned<ItemEntity> {
     }
 
     @Override
+    @NotNull
     public ItemEntity getMaster() {
         return owner;
     }

src/main/java/com/minelittlepony/unicopia/entity/Living.java

@@ -3,6 +3,7 @@ package com.minelittlepony.unicopia.entity;
 import java.util.Optional;
 import java.util.stream.Stream;
 
+import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
 import com.minelittlepony.unicopia.Unicopia;
@@ -81,13 +82,13 @@ public abstract class Living<T extends LivingEntity> implements Equine<T>, Caste
     }
 
     @Override
+    @NotNull
     public T getMaster() {
         return entity;
     }
 
     @Override
     public void tick() {
-
         try {
             getSpellSlot().forEach(spell -> Operation.ofBoolean(spell.tick(this, Situation.BODY)), true);
         } catch (Exception e) {

src/main/java/com/minelittlepony/unicopia/entity/behaviour/Disguise.java

@@ -101,7 +101,7 @@ public interface Disguise extends FlightType.Provider, PlayerDimensions.Provider
             player.setInvisible(true);
 
             if (entity instanceof Owned) {
-                ((Owned<LivingEntity>)entity).setMaster(player.getMaster());
+                ((Owned<LivingEntity>)entity).setMaster(player);
             }
 
             if (entity instanceof PlayerEntity) {

src/main/java/com/minelittlepony/unicopia/entity/behaviour/MobBehaviour.java

@@ -27,7 +27,7 @@ public class MobBehaviour<T extends MobEntity> extends EntityBehaviour<T> {
 
     protected LivingEntity findTarget(Pony player, T entity) {
         return RayTraceHelper.<LivingEntity>findEntity(player.getEntity(), 6, 1,
-                e -> e instanceof LivingEntity && e != entity && e != player.getMaster())
+                e -> e instanceof LivingEntity && e != entity && !player.isOwnedBy(e))
                 .orElseGet(() -> getDummy(entity));
     }
 

src/main/java/com/minelittlepony/unicopia/entity/player/dummy/DummyClientPlayerEntity.java

@@ -3,6 +3,7 @@ package com.minelittlepony.unicopia.entity.player.dummy;
 import java.util.List;
 
 import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 
 import com.minelittlepony.unicopia.InteractionManager;
 import com.minelittlepony.unicopia.Owned;
@@ -66,6 +67,7 @@ public class DummyClientPlayerEntity extends AbstractClientPlayerEntity implemen
     }
 
     @Override
+    @Nullable
     public PlayerEntity getMaster() {
         return owner;
     }

src/main/java/com/minelittlepony/unicopia/entity/player/dummy/DummyPlayerEntity.java

@@ -1,5 +1,7 @@
 package com.minelittlepony.unicopia.entity.player.dummy;
 
+import org.jetbrains.annotations.Nullable;
+
 import com.minelittlepony.unicopia.InteractionManager;
 import com.minelittlepony.unicopia.Owned;
 import com.mojang.authlib.GameProfile;
@@ -23,6 +25,7 @@ public class DummyPlayerEntity extends PlayerEntity implements Owned<PlayerEntit
     }
 
     @Override
+    @Nullable
     public PlayerEntity getMaster() {
         return owner;
     }

src/main/java/com/minelittlepony/unicopia/entity/player/dummy/DummyServerPlayerEntity.java

@@ -1,5 +1,7 @@
 package com.minelittlepony.unicopia.entity.player.dummy;
 
+import org.jetbrains.annotations.Nullable;
+
 import com.minelittlepony.unicopia.InteractionManager;
 import com.minelittlepony.unicopia.Owned;
 import com.mojang.authlib.GameProfile;
@@ -29,6 +31,7 @@ public class DummyServerPlayerEntity extends ServerPlayerEntity implements Owned
     }
 
     @Override
+    @Nullable
     public PlayerEntity getMaster() {
         return owner;
     }

src/main/java/com/minelittlepony/unicopia/item/FriendshipBraceletItem.java

@@ -1,6 +1,7 @@
 package com.minelittlepony.unicopia.item;
 
 import java.util.List;
+import java.util.UUID;
 
 import org.jetbrains.annotations.Nullable;
 
@@ -41,6 +42,7 @@ public class FriendshipBraceletItem extends WearableItem implements DyeableItem,
             ItemStack result = stack.copy();
             result.setCount(1);
             result.getOrCreateNbt().putString("issuer", player.getName().asString());
+            result.getOrCreateNbt().putUuid("issuer_id", player.getUuid());
 
             if (!player.getAbilities().creativeMode) {
                 stack.decrement(1);
@@ -65,7 +67,7 @@ public class FriendshipBraceletItem extends WearableItem implements DyeableItem,
     @Environment(EnvType.CLIENT)
     public void appendTooltip(ItemStack stack, @Nullable World world, List<Text> list, TooltipContext tooltipContext) {
         if (isSigned(stack)) {
-            list.add(new TranslatableText("item.unicopia.friendship_bracelet.issuer", getSignature(stack)));
+            list.add(new TranslatableText("item.unicopia.friendship_bracelet.issuer", getSignatorName(stack)));
         }
         if (isGlowing(stack)) {
             list.add(new TranslatableText("item.unicopia.friendship_bracelet.glowing").formatted(Formatting.ITALIC, Formatting.GRAY));
@@ -78,16 +80,25 @@ public class FriendshipBraceletItem extends WearableItem implements DyeableItem,
     }
 
     private boolean checkSignature(ItemStack stack, PlayerEntity player) {
-        return player.getName().asString().contentEquals(getSignature(stack));
+        return checkSignature(stack, player.getUuid());
+    }
+
+    private boolean checkSignature(ItemStack stack, UUID player) {
+        return player.equals(getSignatorId(stack));
     }
 
     @Nullable
-    public static String getSignature(ItemStack stack) {
+    public static String getSignatorName(ItemStack stack) {
         return isSigned(stack) ? stack.getNbt().getString("issuer") : null;
     }
 
+    @Nullable
+    public static UUID getSignatorId(ItemStack stack) {
+        return isSigned(stack) ? stack.getNbt().getUuid("issuer_id") : null;
+    }
+
     public static boolean isSigned(ItemStack stack) {
-        return stack.hasNbt() && stack.getNbt().contains("issuer");
+        return stack.hasNbt() && stack.getNbt().contains("issuer_id");
     }
 
     public static boolean isSignedBy(ItemStack stack, PlayerEntity player) {
@@ -95,13 +106,18 @@ public class FriendshipBraceletItem extends WearableItem implements DyeableItem,
                 && ((FriendshipBraceletItem)stack.getItem()).checkSignature(stack, player);
     }
 
-    public static boolean isComrade(Caster<?> caster, Entity entity) {
-        Entity master = caster.getMaster();
-        if (master instanceof PlayerEntity && entity instanceof LivingEntity) {
-            return isSignedBy(((LivingEntity)entity).getOffHandStack(), (PlayerEntity)master)
-                    || isSignedBy(((LivingEntity)entity).getEquippedStack(EquipmentSlot.CHEST), (PlayerEntity)master);
-        }
+    public static boolean isSignedBy(ItemStack stack, UUID player) {
+        return stack.getItem() instanceof FriendshipBraceletItem
+                && ((FriendshipBraceletItem)stack.getItem()).checkSignature(stack, player);
+    }
 
+    public static boolean isComrade(Caster<?> caster, Entity entity) {
+        if (entity instanceof LivingEntity) {
+            return caster.getMasterId().filter(id -> {
+                return isSignedBy(((LivingEntity)entity).getOffHandStack(), id)
+                        || isSignedBy(((LivingEntity)entity).getEquippedStack(EquipmentSlot.CHEST), id);
+            }).isPresent();
+        }
         return false;
     }
 }

src/main/java/com/minelittlepony/unicopia/mixin/MixinDamageSource.java

@@ -15,13 +15,14 @@ import net.minecraft.text.TranslatableText;
 
 @Mixin(DamageSource.class)
 abstract class MixinDamageSource {
+    @SuppressWarnings("unchecked")
     @Inject(method = "getDeathMessage", at = @At("RETURN"), cancellable = true)
     private void onGetDeathMessage(LivingEntity entity, CallbackInfoReturnable<Text> info) {
         Equine.of(entity).map(Equine::getAttacker).ifPresent(attacker -> {
             DamageSource self = (DamageSource)(Object)this;
 
             Entity prime = entity.getPrimeAdversary();
-            if (prime != null && !(attacker instanceof Owned<?> && ((Owned<?>)attacker).getMaster() == prime)) {
+            if (prime != null && !(attacker instanceof Owned<?> && ((Owned<Entity>)attacker).isOwnedBy(prime))) {
                 info.setReturnValue(new TranslatableText("death.attack.generic.and_also", info.getReturnValue(), attacker.getDisplayName()));
                 return;
             }

src/main/java/com/minelittlepony/unicopia/projectile/MagicProjectileEntity.java

@@ -66,7 +66,7 @@ public class MagicProjectileEntity extends ThrownItemEntity implements Caster<Li
         super(type, world);
     }
 
-    public MagicProjectileEntity(World world, LivingEntity thrower) {
+    public MagicProjectileEntity(World world, @Nullable LivingEntity thrower) {
         super(UEntities.THROWN_ITEM, thrower, world);
     }
 
@@ -103,6 +103,7 @@ public class MagicProjectileEntity extends ThrownItemEntity implements Caster<Li
     }
 
     @Override
+    @Nullable
     public LivingEntity getMaster() {
         return (LivingEntity)getOwner();
     }

src/main/java/com/minelittlepony/unicopia/util/MagicalDamageSource.java

@@ -31,7 +31,7 @@ public class MagicalDamageSource extends EntityDamageSource {
         return new MagicalDamageSource(type, null, null, false, false);
     }
 
-    public static DamageSource create(String type, LivingEntity source) {
+    public static DamageSource create(String type, @Nullable LivingEntity source) {
         return new MagicalDamageSource(type, source, null, false, false);
     }