How Do I Make A Modded Mob Shoot Wither Skulls or Other Projectiles

You need to give it direction and power, so it can move ^^

You can also use default shooting option (it's on 'behaviour' part of mob, if I'm not mistaken) and use command to convert that projectile into wither skull. I tried using that option in MCreator 2020.2 which doesn't support custom projectiles, and it works somehow, so it should work even better in newer versions, when you can customize projectiles much more!

Toma, can you explain what you did with code, etc since I'm trying to do the same thing but I don't understand how you did it