--- a/net/minecraft/server/EntityTypes.java
+++ b/net/minecraft/server/EntityTypes.java
@@ -130,7 +130,7 @@
     private MinecraftKey bi;
     private final EntitySize bj;
 
-    private static <T extends Entity> EntityTypes<T> a(String s, EntityTypes.a<T> entitytypes_a) {
+    private static <T extends Entity> EntityTypes<T> a(String s, EntityTypes.a entitytypes_a) { // CraftBukkit - decompile error
         return (EntityTypes) IRegistry.a((IRegistry) IRegistry.ENTITY_TYPE, s, (Object) entitytypes_a.a(s));
     }
 
@@ -159,10 +159,16 @@
 
     @Nullable
     public T spawnCreature(World world, @Nullable NBTTagCompound nbttagcompound, @Nullable IChatBaseComponent ichatbasecomponent, @Nullable EntityHuman entityhuman, BlockPosition blockposition, EnumMobSpawn enummobspawn, boolean flag, boolean flag1) {
+        // CraftBukkit start
+        return this.spawnCreature(world, nbttagcompound, ichatbasecomponent, entityhuman, blockposition, enummobspawn, flag, flag1, org.bukkit.event.entity.CreatureSpawnEvent.SpawnReason.SPAWNER_EGG);
+    }
+
+    @Nullable
+    public T spawnCreature(World world, @Nullable NBTTagCompound nbttagcompound, @Nullable IChatBaseComponent ichatbasecomponent, @Nullable EntityHuman entityhuman, BlockPosition blockposition, EnumMobSpawn enummobspawn, boolean flag, boolean flag1, org.bukkit.event.entity.CreatureSpawnEvent.SpawnReason spawnReason) {
         T t0 = this.b(world, nbttagcompound, ichatbasecomponent, entityhuman, blockposition, enummobspawn, flag, flag1);
 
-        world.addEntity(t0);
-        return t0;
+        return world.addEntity(t0, spawnReason) ? t0 : null; // Don't return an entity when CreatureSpawnEvent is canceled
+        // CraftBukkit end
     }
 
     @Nullable
@@ -328,7 +334,7 @@
             }
 
             return entity;
-        }).orElse((Object) null);
+        }).orElse(null); // CraftBukkit - decompile error
     }
 
     private static Optional<Entity> b(NBTTagCompound nbttagcompound, World world) {
@@ -345,7 +351,8 @@
     }
 
     public int getUpdateInterval() {
-        return this != EntityTypes.PLAYER && this != EntityTypes.EVOKER_FANGS ? (this == EntityTypes.EYE_OF_ENDER ? 4 : (this == EntityTypes.FISHING_BOBBER ? 5 : (this != EntityTypes.SMALL_FIREBALL && this != EntityTypes.DRAGON_FIREBALL && this != EntityTypes.FIREBALL && this != EntityTypes.WITHER_SKULL && this != EntityTypes.SNOWBALL && this != EntityTypes.LLAMA_SPIT && this != EntityTypes.ENDER_PEARL && this != EntityTypes.EGG && this != EntityTypes.POTION && this != EntityTypes.EXPERIENCE_BOTTLE && this != EntityTypes.FIREWORK_ROCKET && this != EntityTypes.TNT ? (this != EntityTypes.ARROW && this != EntityTypes.SPECTRAL_ARROW && this != EntityTypes.TRIDENT && this != EntityTypes.ITEM && this != EntityTypes.FALLING_BLOCK && this != EntityTypes.EXPERIENCE_ORB ? (this != EntityTypes.ITEM_FRAME && this != EntityTypes.LEASH_KNOT && this != EntityTypes.PAINTING && this != EntityTypes.AREA_EFFECT_CLOUD && this != EntityTypes.END_CRYSTAL ? 3 : Integer.MAX_VALUE) : 20) : 10))) : 2;
+        // CraftBukkit - SPIGOT-3729: track area effect clouds
+        return this != EntityTypes.PLAYER && this != EntityTypes.EVOKER_FANGS ? (this == EntityTypes.EYE_OF_ENDER ? 4 : (this == EntityTypes.FISHING_BOBBER ? 5 : (this != EntityTypes.SMALL_FIREBALL && this != EntityTypes.DRAGON_FIREBALL && this != EntityTypes.FIREBALL && this != EntityTypes.WITHER_SKULL && this != EntityTypes.SNOWBALL && this != EntityTypes.LLAMA_SPIT && this != EntityTypes.ENDER_PEARL && this != EntityTypes.EGG && this != EntityTypes.POTION && this != EntityTypes.EXPERIENCE_BOTTLE && this != EntityTypes.FIREWORK_ROCKET && this != EntityTypes.TNT ? (this != EntityTypes.ARROW && this != EntityTypes.SPECTRAL_ARROW && this != EntityTypes.TRIDENT && this != EntityTypes.ITEM && this != EntityTypes.FALLING_BLOCK && this != EntityTypes.EXPERIENCE_ORB ? (this != EntityTypes.ITEM_FRAME && this != EntityTypes.LEASH_KNOT && this != EntityTypes.PAINTING && this != EntityTypes.END_CRYSTAL ? 3 : Integer.MAX_VALUE) : 20) : 10))) : 2;
     }
 
     public boolean isDeltaTracking() {
@@ -377,7 +384,7 @@
             this.f = enumcreaturetype == EnumCreatureType.CREATURE || enumcreaturetype == EnumCreatureType.MISC;
         }
 
-        public static <T extends Entity> EntityTypes.a<T> a(EntityTypes.b<T> entitytypes_b, EnumCreatureType enumcreaturetype) {
+        public static <T extends Entity> EntityTypes.a<T> a(EntityTypes.b entitytypes_b, EnumCreatureType enumcreaturetype) { // CraftBukkit - decompile error
             return new EntityTypes.a<>(entitytypes_b, enumcreaturetype);
         }