Only interact with the datatracker after it's safe to do so

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

@@ -70,13 +70,17 @@ public class Creature extends Living<LivingEntity> implements WeaklyOwned.Mutabl
     public Creature(LivingEntity entity) {
         super(entity, EFFECT);
         physics = new EntityPhysics<>(entity, GRAVITY);
+        addTicker(physics);
+        addTicker(this::updateConsumption);
+    }
+
+    @Override
+    public void initDataTracker() {
+        super.initDataTracker();
         entity.getDataTracker().startTracking(MASTER, owner.toNBT());
         entity.getDataTracker().startTracking(EATING, 0);
         entity.getDataTracker().startTracking(DISCORDED, false);
         entity.getDataTracker().startTracking(SMITTEN, false);
-
-        addTicker(physics);
-        addTicker(this::updateConsumption);
     }
 
     @Override

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

@@ -28,16 +28,8 @@ public class EntityPhysics<T extends Entity> implements Physics, Copyable<Entity
     private float lastGravity = 1;
 
     public EntityPhysics(T entity, TrackedData<Float> gravity) {
-        this(entity, gravity, true);
-    }
-
-    public EntityPhysics(T entity, TrackedData<Float> gravity, boolean register) {
         this.entity = entity;
         this.gravity = gravity;
-
-        if (register) {
-            this.entity.getDataTracker().startTracking(gravity, 1F);
-        }
     }
 
     @Override

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

@@ -19,6 +19,8 @@ public interface Equine<T extends Entity> extends NbtSerialisable, Tickable, Pro
 
     void setSpecies(Race race);
 
+    void initDataTracker();
+
     /**
      * Called at the beginning of an update cycle.
      */

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

@@ -41,8 +41,12 @@ public class ItemImpl implements Equine<ItemEntity> {
     public ItemImpl(ItemEntity owner) {
         this.entity = owner;
         this.physics = new ItemPhysics(owner);
-        owner.getDataTracker().startTracking(ITEM_GRAVITY, 1F);
+    }
-        owner.getDataTracker().startTracking(ITEM_RACE, Race.REGISTRY.getId(Race.HUMAN).toString());
+
+    @Override
+    public void initDataTracker() {
+        entity.getDataTracker().startTracking(ITEM_GRAVITY, 1F);
+        entity.getDataTracker().startTracking(ITEM_RACE, Race.REGISTRY.getId(Race.HUMAN).toString());
     }
 
     @Override

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

@@ -4,7 +4,7 @@ import net.minecraft.entity.ItemEntity;
 
 class ItemPhysics extends EntityPhysics<ItemEntity> {
     public ItemPhysics(ItemEntity entity) {
-        super(entity, ItemImpl.ITEM_GRAVITY, false);
+        super(entity, ItemImpl.ITEM_GRAVITY);
     }
 
     @Override

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

@@ -111,12 +111,15 @@ public abstract class Living<T extends LivingEntity> implements Equine<T>, Caste
     protected Living(T entity, TrackedData<NbtCompound> effect) {
         this.entity = entity;
         this.effectDelegate = new EffectSync(this, effect);
-
         this.sneakingHeuristic = addTicker(new Interactable(entity::isSneaking));
         this.landedHeuristic = addTicker(new Interactable(entity::isOnGround));
         this.jumpingHeuristic = addTicker(new Interactable(((LivingEntityDuck)entity)::isJumping));
+    }
 
-        entity.getDataTracker().startTracking(effect, new NbtCompound());
+    @Override
+    public void initDataTracker() {
+        effectDelegate.initDataTracker();
+        entity.getDataTracker().startTracking(Creature.GRAVITY, 1F);
         entity.getDataTracker().startTracking(CARRIER_ID, Optional.empty());
     }
 

src/main/java/com/minelittlepony/unicopia/entity/player/Acrobatics.java

@@ -41,12 +41,13 @@ public class Acrobatics implements Tickable, NbtSerialisable {
     public Acrobatics(Pony pony) {
         this.pony = pony;
         this.entity = pony.asEntity();
-
-        entity.getDataTracker().startTracking(HANGING_POSITION, Optional.empty());
-
         pony.addTicker(this::checkDislodge);
     }
 
+    public void initDataTracker() {
+        entity.getDataTracker().startTracking(HANGING_POSITION, Optional.empty());
+    }
+
     public boolean isImmobile() {
         return isFloppy() && entity.isOnGround();
     }

src/main/java/com/minelittlepony/unicopia/entity/player/ManaContainer.java

@@ -38,6 +38,10 @@ class ManaContainer implements MagicReserves, Tickable, NbtSerialisable, Copyabl
         });
     }
 
+    public void initDataTracker() {
+        bars.values().forEach(BarInst::initDataTracker);
+    }
+
     protected BarInst addBar(String name, BarInst bar) {
         bars.put(name, bar);
         return bar;
@@ -164,7 +168,12 @@ class ManaContainer implements MagicReserves, Tickable, NbtSerialisable, Copyabl
             this.marker = marker;
             this.max = max;
             this.trailingValue = initial;
-            pony.asEntity().getDataTracker().startTracking(marker, getMax() * initial);
+            this.prevTrailingValue = initial;
+            this.prevValue = initial;
+        }
+
+        public void initDataTracker() {
+            pony.asEntity().getDataTracker().startTracking(marker, max * trailingValue);
         }
 
         @Override

src/main/java/com/minelittlepony/unicopia/entity/player/PlayerLevelStore.java

@@ -21,7 +21,6 @@ class PlayerLevelStore implements Levelled.LevelStore {
         this.dataEntry = dataEntry;
         this.upgradeMana = upgradeMana;
         this.levelUpSound = levelUpSound;
-        pony.asEntity().getDataTracker().startTracking(dataEntry, 0);
     }
 
     @Override

src/main/java/com/minelittlepony/unicopia/entity/player/Pony.java

@@ -125,15 +125,23 @@ public class Pony extends Living<PlayerEntity> implements Copyable<Pony>, Update
         this.corruption = new PlayerLevelStore(this, CORRUPTION, false, USounds.ENTITY_PLAYER_CORRUPTION);
         this.mana = addTicker(new ManaContainer(this));
 
-        player.getDataTracker().startTracking(RACE, Race.DEFAULT_ID);
-        player.getDataTracker().startTracking(SUPPRESSED_RACE, Race.DEFAULT_ID);
-
         addTicker(this::updateAnimations);
         addTicker(this::updateBatPonyAbilities);
         addTicker(this::updateCorruptionDecay);
         addTicker(new PlayerAttributes(this));
     }
 
+    @Override
+    public void initDataTracker() {
+        super.initDataTracker();
+        acrobatics.initDataTracker();
+        mana.initDataTracker();
+        entity.getDataTracker().startTracking(LEVEL, 0);
+        entity.getDataTracker().startTracking(CORRUPTION, 0);
+        entity.getDataTracker().startTracking(RACE, Race.DEFAULT_ID);
+        entity.getDataTracker().startTracking(SUPPRESSED_RACE, Race.DEFAULT_ID);
+    }
+
     public static void registerAttributes(DefaultAttributeContainer.Builder builder) {
         builder.add(UEntityAttributes.EXTRA_MINING_SPEED);
         builder.add(UEntityAttributes.ENTITY_GRAVITY_MODIFIER);

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

@@ -19,12 +19,14 @@ import com.minelittlepony.unicopia.entity.Living;
 import com.minelittlepony.unicopia.entity.duck.EntityDuck;
 
 import net.minecraft.entity.Entity;
+import net.minecraft.entity.EntityType;
 import net.minecraft.entity.ItemEntity;
 import net.minecraft.entity.Entity.PositionUpdater;
 import net.minecraft.entity.Entity.RemovalReason;
 import net.minecraft.fluid.Fluid;
 import net.minecraft.item.ItemStack;
 import net.minecraft.registry.tag.TagKey;
+import net.minecraft.world.World;
 
 @Mixin(Entity.class)
 abstract class MixinEntity implements EntityDuck {
@@ -64,6 +66,14 @@ abstract class MixinEntity implements EntityDuck {
         return self.hasVehicle() && self.getVehicle() instanceof LavaAffine affine && affine.isLavaAffine();
     }
 
+
+    @Inject(method = "<init>", at = @At(value = "INVOKE", target = "net/minecraft/entity/Entity.initDataTracker()V"))
+    private void onInstanceInit(EntityType<?> type, World world, CallbackInfo info) {
+        if (this instanceof Equine.Container c) {
+            c.get().initDataTracker();
+        }
+    }
+
     @Inject(method = "isFireImmune", at = @At("HEAD"), cancellable = true)
     private void onIsFireImmune(CallbackInfoReturnable<Boolean> info) {
         if (isLavaAffine() || (this instanceof Equine.Container c) && c.get().getCompositeRace().includes(Race.KIRIN)) {

src/main/java/com/minelittlepony/unicopia/network/datasync/EffectSync.java

@@ -43,6 +43,10 @@ public class EffectSync implements SpellContainer, NbtSerialisable {
         this.param = param;
     }
 
+    public void initDataTracker() {
+        owner.asEntity().getDataTracker().startTracking(param, new NbtCompound());
+    }
+
     public boolean tick(Situation situation) {
         return tick(spell -> {
             if (spell.isDying()) {

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

@@ -67,7 +67,7 @@ public class MagicProjectileEntity extends ThrownItemEntity implements Caster<Ma
 
     private final EffectSync effectDelegate = new EffectSync(this, EFFECT);
 
-    private final EntityPhysics<MagicProjectileEntity> physics = new EntityPhysics<>(this, GRAVITY, false);
+    private final EntityPhysics<MagicProjectileEntity> physics = new EntityPhysics<>(this, GRAVITY);
 
     private final EntityReference<Entity> homingTarget = new EntityReference<>();
     private EntityReference<LivingEntity> owner;