Just cleared Porin at very hard.
Basically teamed up with Odin. Store skills for every turn, easy win.
Rainbow Keeper kind of did nothing except to provide high attack. Amaterasu is overkill as damage taken with Odin's skill does not exceed 2k, so Siren should suffice. Black Magician + Dark Resist = all creeps die except for grass devils and slimes, both are great for wasting turns to regain the skills.