There is a simple trick to kill Uber Prinny Baal. You need a Scout or anyone with the Geo Change skill. Go to the Lord of Terror map, in Baal Castle, and have the person with Geo Change skill use it. If there are no "Damage 20%" or "Invincibility" Geo Panels, then hit "Quit" on the menu screen and try again. Keep Baal on the Damage 20% squares to have him die in 5 turns. Or, if you can do damage to him, wait for invincibility. It helps to steal Baal's items to do damage.