Quite frankly, you should be able to beat most anything an average party level of ~60, and Tiamat isn't as hard as he's made out to be. Jet Fire carries a Heat status attachment, so equip everyone with Body Temp to negate the effect -- that's really its main skill. The ____ Absorb abilities are turn-wasters as far as the boss is concerned, and if you have any Shock/Frog Drop/Dragon's Crest abilities powered-up, it's as good as dead. 'Sides that, watch out for the Yannish 'Snort' ability which ejects a character from battle immediately. May not even use it, but it's still inconveniencing.