Milotic + Blissey Combo

Blissey is a great Pokemon due to it having more HP than any other Pokemon, and also having very good Special Defense. The problem is its low Defense. A strong, physical Fighting type move can OHKO it. To fix this, in a Double Battle, make Blissey hold a Flame Orb or Toxic Orb, or something like that that will give it a status condition. On the first turn, use Skill Swap to trade abilities with your Milotic. Blissey will then have Milotic's ability Marvel Scale, which raises the Pokemon's Defense when it has a status condition. And since it is burned, its Defense will be raised.