so I got Wadatsumi (Mythical) to about 10% of his HP before he OH me ruthlessly. I decided popping a Persephone when he was around 60% left (even though there were only three wood and three fire aside from light, heal, and dark), since if he got healed by it I can just easily do it again (yeeeaaaah 2/6.25/2.5 teams).
Now I know, I guess. I can keep chipping away at his health until he can be finished off, I guess.
Also, Cyclone Devil Dragon is incredible in Wadatsumi what with all the water conversions -and- the combo with Byakko's active.