I just beat him in one turn at level 14 before he could even do anything, after many many unsuccessful attempts. I was worried about the level difference because he was level 15 and the difference between levels is very noticeable in this game, but I sent in Madora to use Flurry, she critted on 3 of the hits and that took out most of his health. When he tried to run past her to the middle to summon his lil friends, an attack of opportunity arose and he died. This obviously may not OHKO him like it did for me (critical chance is the only reason it worked) but it'll put a big dent in his health regardless. Hope this helps!
