You don't have to target mobs for most abilities. If you use a melee attack it'll be used against the mob you're targeting if they're in melee range. If they're not or if you don't have a target, the attack will be used on some nearby mob. If you use fireball without a target, it'll go in the direction you're facing.
Having a target is only necessary for shooting arrows, but you could easily make them work like fireball if you didn't want your game to use targeting.
Having a target is only necessary for shooting arrows, but you could easily make them work like fireball if you didn't want your game to use targeting.