Once you have gotten to a certain point in the game when you use the "drive" option you will change into a heartless type sora he is covered in a black shadowy aura and is extremely fast,and can do huge combows,byt his attacks are weak,getting him in a battle where you need to dodge attacks is a good thing,it uses all drives,and you cant revert untill they are all gone,but it can be usefull where you need to get battles done in a certain time limit.