Attacks: Giga Breath, Drain Bark, Poison Ball
This is a tough boss, so make sure you have everyone standing in the shape of a square. Karin in the back,Crazy Pizza or your stronger golem next to her and Raigar and Astuma in the front. Crazy Pizza, Atsuma, and Raigar attack (Raiger also needs to cast shield on the people he can so they dont take as much damage) and Karin heals the person next to her, herself, and the person in front of her (if he doesn't do much damage and your people still have a lot of health and he's close enough then she can attack also.) Make sure you use Atsuma's Summon Phoenix when you can. It may take a couple of tries, but you'll eventually be able to defeat him for the achievement.