Use a team that consists of Jean Grey and Carnage (bonus downloadable content required; also Songbird and Gambit round out the team nicely). As Grey, constantly use her "Pyrokine Blast" (R2 + Square) and dodging. This will quickly fill up your fusion meter while avoiding damage. Once your fusion meter is full, perform a "targeted" fusion with Grey and Carnage. This fusion attacks one target twice (unlike other target attacks), and can even damage or knock out another Boss close by, while getting health pickups for successful attacks. Repeat the process until the mission clears. If done well, you can unlock Carnage's alternate costume, and get two achievements or trophies specific to this mission with relative ease.