|Grandia II Boss|
Valmar's Tongue is one of the seven pieces of Valmar, it was removed during The Battle of Good and Evil and sealed within the Liligue Cave. The seal was eventually broken and possessed the gluttonous Skyway Manager Gadan.
First attack his head with your most powerful attacks to deal as much damage as possible. Next turn, finish the head and that should cancel his Snooze and Burnflame skills. Then deal with his hands with any remaining moves you've left and destroy his hands one by one.
His four body skills are more than enough to defend himself and deal damage, so be careful. Your SP and MP should be pretty much used up but if you have something left use it, if not just attack him with combo or items. But always let one character do Critical all the time, it won't cancel all his skills but will give some time. If you're in a stable position keep attacking him and keep using Critical that should be enough to kill him.