Ah, Deadbeard (Golden Sun)
I fought this guy twice over my history of gaming. The first time the battle simply was a Very Long sequence of doing damage and staying healed. I had to use my Psy Crystals, which I didn't want to use, but I figured what the hell.
The Second time, more recently, I absolutely kicked his ass. I don't know why, but I guess I just busted out with all the right summons and attacks. For instance, I knew that time that he was strong against Water, so I didn't use Mia to attack at ALL, she was 100% healer/assist. He's weak against Earth, so Isaac was particularly valuable. Many earth summons and whatnot.
I ended up accidentally killing him with the overkill method. I used the Sap djinni on him and was intending to build up another summon, but he just turned multi-colored and gave me 20% more exp and gold. It was awesome.