Some more cleanup

src/main/java/org/bukkit/Art.java

@@ -106,7 +106,20 @@ public abstract class Art extends OldEnum<Art> implements Keyed {
     @Deprecated
     @Nullable
     public static Art getById(int id) {
-        return BY_ID.get(id);
+        Art art = BY_ID.get(id);
+
+        if (art != null) {
+            return art;
+        }
+
+        for (Art other : Registry.ART) {
+            if (other.getId() == id) {
+                BY_ID.put(id, other);
+                return other;
+            }
+        }
+
+        return null;
     }
 
     /**

src/main/java/org/bukkit/block/banner/PatternType.java

@@ -88,15 +88,19 @@ public abstract class PatternType extends OldEnum<PatternType> implements Keyed
             return null;
         }
 
-        return byString.computeIfAbsent(identifier, id -> {
-            for (PatternType patternType : Registry.BANNER_PATTERN) {
-                if (identifier.equals(patternType.getIdentifier())) {
-                    return patternType;
-                }
-            }
+        PatternType patternType = byString.get(identifier);
+        if (patternType != null) {
+            return patternType;
+        }
 
-            return null;
-        });
+        for (PatternType type : Registry.BANNER_PATTERN) {
+            if (identifier.equals(type.getIdentifier())) {
+                byString.put(identifier, type);
+                return type;
+            }
+        }
+
+        return null;
     }
 
     /**

src/main/java/org/bukkit/entity/EntityType.java

@@ -337,6 +337,14 @@ public abstract class EntityType<E extends Entity> extends OldEnum<EntityType<E>
     @Nullable
     public abstract Class<E> getEntityClass();
 
+    /**
+     * Gets if this EntityType is enabled by feature in a world.
+     *
+     * @param world the world to check
+     * @return true if this EntityType can be used to spawn an Entity for this World.
+     */
+    public abstract boolean isEnabledByFeature(@NotNull World world);
+
     /**
      * Gets the entity type name.
      *
@@ -478,14 +486,4 @@ public abstract class EntityType<E extends Entity> extends OldEnum<EntityType<E>
 
         return from;
     }
-
-    /**
-     * Gets if this EntityType is enabled by feature in a world.
-     *
-     * @param world the world to check
-     * @return true if this EntityType can be used to spawn an Entity for this World.
-     */
-    public boolean isEnabledByFeature(@NotNull World world) {
-        return Bukkit.getDataPackManager().isEnabledByFeature(this, world);
-    }
 }

src/main/java/org/bukkit/potion/PotionEffectType.java

@@ -208,9 +208,7 @@ public abstract class PotionEffectType implements Keyed {
      * @see PotionBrewer#createEffect(PotionEffectType, int, int)
      */
     @NotNull
-    public PotionEffect createEffect(int duration, int amplifier) {
-        return new PotionEffect(this, isInstant() ? 1 : (int) (duration * getDurationModifier()), amplifier);
-    }
+    public abstract PotionEffect createEffect(int duration, int amplifier);
 
     /**
      * Returns whether the effect of this type happens once, immediately.
@@ -260,9 +258,11 @@ public abstract class PotionEffectType implements Keyed {
      *
      * @param key key to fetch
      * @return Resulting PotionEffectType, or null if not found
+     * @deprecated only for backwards compatibility, use {@link Registry#get(NamespacedKey)} instead.
      */
     @Contract("null -> null")
     @Nullable
+    @Deprecated
     public static PotionEffectType getByKey(@Nullable NamespacedKey key) {
         return Registry.POTION_EFFECT_TYPE.get(key);
     }
@@ -277,7 +277,20 @@ public abstract class PotionEffectType implements Keyed {
     @Deprecated
     @Nullable
     public static PotionEffectType getById(int id) {
-        return ID_MAP.get(id);
+        PotionEffectType type = ID_MAP.get(id);
+
+        if (type != null) {
+            return type;
+        }
+
+        for (PotionEffectType other : Registry.POTION_EFFECT_TYPE) {
+            if (other.getId() == id) {
+                ID_MAP.put(id, other);
+                return other;
+            }
+        }
+
+        return null;
     }
 
     /**

src/main/java/org/bukkit/potion/PotionEffectTypeWrapper.java

@@ -37,6 +37,12 @@ public class PotionEffectTypeWrapper extends PotionEffectType {
         return PotionEffectType.getByKey(getKey());
     }
 
+    @NotNull
+    @Override
+    public PotionEffect createEffect(int duration, int amplifier) {
+        return getType().createEffect(duration, amplifier);
+    }
+
     @Override
     public boolean isInstant() {
         return getType().isInstant();

src/main/java/org/bukkit/potion/PotionType.java

@@ -11,7 +11,7 @@ import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
 /**
- * This enum reflects and matches each potion state that can be obtained from
+ * This class reflects and matches each potion state that can be obtained from
  * the Creative mode inventory
  */
 public abstract class PotionType extends OldEnum<PotionType> implements Keyed {