basically it's all in the title. Your very own god boss doesn't nessessarily have to correspond to a specific final fantasy but would obviously have to follow the basic final fantasy battle system.

Your boss should be defeatable!!!!! Make him as hard as you like, in fact, make him next to impossible if you desire. but there must be a way of defeating him. He needs a name, a breed of monster or whatever you choose for him to be, an approach on how he attacks you, and obviously a set of attacks.

I have one i think would be great but i want to see what you come up with first