~20 minute Rainbow Keeper (Master) team:
So the theory turned out to be correct. Two keeper encounters in rounds 4 and 5. You need Amaterasu Ohkami/Siren/Alraune & Green Odin leaders, and a team of monsters all with charged attack skills. Once you get to the keepers, forget about planning matches and combos; the goal is to make matches with any orbs as quickly as possible to build up skills and heal yourself.
Because of Green Odin and the long interval between the keepers' attacks, you're never in any danger of dying--Alraune or Siren are just as effective if you're smart about the first three rounds.
My team has a relatively high cost (113) so not everyone will be able to do it as quickly, but as you can see most of the monsters I used are not even leveled. They can be switched out with lower cost/lower evolved forms of 'lil dragons or anything with charged attack skills. You may not breeze by in 20 minutes, but it sure won't take an hour+ anymore.
Emphasis on this being one place to forget planning and orb chaining once you get to the bosses; it does jack shit. So besides the obvious competent healer, you're looking for anything similar to the following to go on your team.
Monster - Skill:
- Green Odin - 20x light attribute attack (required leader)
- Graviton Earth Dragon - Enormous wood attack
- Ice Mechdragon - Critical water attack
- Meteor Volcano Dragon - Enormous fire attack
- Divinegon - Light attack of 10x your attack
