As some parts of the X-Box 360 version of MUA 2 are harder than the rest, I would like to see a tactic for what you thought was the hardest part of the game.
For Example: The hardest part for me was the battle against Colossus and Dagger. What I did was got the X-Men team ( :cable:, :storm:, :wolverine:, and :deadpool:.) I maxed out Wolverine's healing factor and just kept building up the fusions. Whenever Wolvie got low on health I would just run away. Also, I recommend picking up the 3 star fusion for extra fusions. I would work on Dagger first then focus on Colossus. (Chances are even if you attempt to kill Colossus first, Dagger will die before him.)
For me, the hardest part was the whole last act on the hardest difficulty. But if you have a good team (who you love to use and good at using) with maximum level and good team boosts, well you can do it :D