I would say try one of those dragons again. To go outside the box, I'd say try Huntress or Tribal if you have one of those or even a high level Air dragon. To even go more exotic, if you have Defender, Helios or Odyssey maybe try them. According to the battle chart Fairytale and Mythic types are good against Rainbow types. If you have a gold producing dragon such as Gold Horizon, it may be effective too.