Well, I tried using both of Jean Gray's powers that I had unlocked, and neither did squat. No damage to Juggernaut (yes, his helmet had already come off), and no effect that I could tell.

I tried playing as Gambit, and actually wasn't doing that bad. Then I got caught in some Sentinel bomb, which knocked off the remaining 2/3 of his health.

I also wasn't bad as Magma during the times I played as her, and only had trouble in the Danger Room because I was getting horribly outnumbered.

I'm honestly looking forward to unlocking Colossus.