How To Make the Drowned For 1.12.2

First things first I want to apologize if I've placed this into the wrong section. If I have, please lead me to the correct section. Secondly, I want to say that I know this topic has been asked about quite a lot (I've looked through almost every forum post about it) but I'm having extreme trouble with a particular mob.

I'm trying to make the Drowned for 1.12.2 but whenever I try to make it swim, it doesn't act like a squid in the sense that it doesn't follow you under the water. It continues to float at the surface. When I try to give it the Squid AI, it doesn't compile correctly and it gives me this.

MCreatorWorkspaces\lost_under_sea\build\sources\main\java\net\mcreator\lost_under_sea\MCreatorDrowned.java:84: error: incompatible types: EntityCustom cannot be converted to EntityCreature
			this.targetTasks.addTask(1, new EntityAIHurtByTarget(this, false));
			                                                     ^
MCreatorWorkspaces\lost_under_sea\build\sources\main\java\net\mcreator\lost_under_sea\MCreatorDrowned.java:85: error: incompatible types: EntityCustom cannot be converted to EntityCreature
			this.tasks.addTask(2, new EntityAIAttackMelee(this, 1, true));
			                                              ^
MCreatorWorkspaces\lost_under_sea\build\sources\main\java\net\mcreator\lost_under_sea\MCreatorDrowned.java:86: error: incompatible types: EntityCustom cannot be converted to EntityCreature
			this.targetTasks.addTask(3, new EntityAINearestAttackableTarget(this, EntityPlayer.class, true, true));
			                                                                ^
MCreatorWorkspaces\lost_under_sea\build\sources\main\java\net\mcreator\lost_under_sea\MCreatorDrowned.java:87: error: incompatible types: EntityCustom cannot be converted to EntityCreature
			this.targetTasks.addTask(4, new EntityAINearestAttackableTarget(this, EntityPlayerMP.class, true, true));
			                                                                ^
MCreatorWorkspaces\lost_under_sea\build\sources\main\java\net\mcreator\lost_under_sea\MCreatorDrowned.java:90: error: incompatible types: EntityCustom cannot be converted to EntityCreature
			this.tasks.addTask(7, new EntityAIWander(this, 0.8));

Is it just not possible yet to create Mob that complex? Or am I just missing something or doing something wrong?