Thunder Reign to stun him (100% effective provided you dont miss), have the next person attack (crit) then all attack, the one after that attack (crit) and all attack again, the 4th person attack (crit) then attack again for Dizzy.
Go nuts on him the next round when he gets up repeat but have the 4th person heal his attack and the third person dizzy (or the second person dizzy if someone died)
only requirements to this strat is Odin and the fact that all 4 characters need to be faster than the Reaper.
D'oh. I feel so silly. I had Odin, however I always went through with the third All-Out since I thought that was the strategy. I didn't know he could get Dizzy'd. That's an interesting way to do it. . . Well, let's see what happens. :3