Immovable/Unpushable Entity? [Solved somewhat]

If you know how to code, override;

EntityLiving::canBePushed

and set it false.

There are two methods that you can use to achieve this;

    @Override
    public boolean canBePushed() {
        return false;
    }

    @Override
    public boolean canBeCollidedWith() {
        return false;
    }

The method LivingEntity::canBePushed returns true if you want the entity to push and be pushed by other entities.

The method LivingEntity::canBeCollidedWith returns true if you want the entity to not be able to go through the entity.

You can use both, it is up to you. Return false if you don't want the above descriptions to happen.