SpawnFakeEntity.java

public class EntityUtil {
  
    public static PacketPlayOutAttachEntity craftAttachPacket(int that, int to) {
        PacketPlayOutAttachEntity packet = new PacketPlayOutAttachEntity();
        setField(getField(packet.getClass(), "a"), that);
        setField(getField(packet.getClass(), "b"), to);
        setField(getField(packet.getClass(), "c"), 0);
    }
    
    public static PacketPlayOutSpawnEntityLiving craftSlimeSpawnPacket(int entityType, int id, Location location, int size) {
        PacketPlayOutSpawnEntityLiving packet = new PacketPlayOutSpawnEntityLiving();
        setField(getField(packet.getClass(), "a"), id);
        setField(getField(packet.getClass(), "b"), entityType);
        setField(getField(packet.getClass(), "c"), floor(location.getX());
        setField(getField(packet.getClass(), "d"), floor(location.getY());
        setField(getField(packet.getClass(), "e"), floor(location.getZ());
        setField(getField(packet.getClass(), "i"), asCompressedAngle(location.getYaw());
        setField(getField(packet.getClass(), "j"), asCompressedAngle(location.getPitch());
        
        DataWatcher watcher = new DataWatcher(null);
        watcher.a(6, (Object) 20.0)
        watcher.a(16, (Object) size);
        
        setField(getField(packet.getClass(), "l"), watcher);
        
        return packet;
    } 
    
    public static int floor(double d) {
        return (int) (d * 32.0D);
    }

    public static byte asCompressedAngle(float f) {
        return (byte) (f * 256.0F / 360.0F);
    }
    
    public static Field getField(Class<?> clazz, String field) {
      try {
        return clazz.getDeclaredField(field);
      } catch (Exception e) {
        e.printStacktrace();
        System.out.println("Failed to retrieve field: \"" + field + "\" from: \"" + clazz.getSimpleName() + "\"");
      }
    } 
    
    public static void setField(Field field, Object instance, Object value) {
      try {
        field.set(instance, value);
      } catch (Exception e) {
        e.printStacktrace();
      }
    }
}