Storm: Calling All X-Men

The main crux of this deck is to get Utopia out to increase your ally limit so you can always keep Gentle , Havok , and Longshot on the table with training upgrades while constantly cycling through the other allies in the deck in order to use their "when played"/"played from hand" abilities. Between "To Me, My X-Men!" and Cerebro you should be able to dig out allies to put on the board, X-Mansion can help keep the ones you want to stick around healthy, and Danger Room can make sure they get Danger Room Training when you do put them into play.

If you don't want to run 42 cards (understandable), Mass Attack can be dropped. It's in there as a "one of" mostly to take advantage of the combination of Storm's Thunderstorm weather support's +1ATK to all characters, and Danger Room Training on the three allies you want to stick around. If everything lines up right, you're looking at a 16 damage play off of just that card. And if you have a Band Together in hand, you've basically just spent two cards for it, which feels really good. If you want to get down to a 40 card deck, you could also lose a Game Time or possibly even Mirage.