Even though it's an RPG, Dullahan from Golden Sun, I don't care what items, levels, psynergy, classes etc. you're carrying are; he is still going to bend you over a couch and beat your ass with a meat tenderizer. His over the top unfair Charon summon and Djinn Storm combo, one decimates your team with possible insta kills, the other pretty much murders your class setup for 9 rounds, he has 16k HP, moves 3 times a turn, everything that isn't a status effect is going to hurt a lot, restores 200 HP a turn, has a drain move that restores 100% HP he steals from 3 of your front party, can end your healer types with Formina Sage.
Now imagine getting that three times in a row in the battle arena.
I have heard forging Excaliburs help, but I don't have that kind of luck, 5% forge chance, yeah screw that.