Mutant protectors Colossus

Use cards like Armored Vest, to help Colossus keep his Tough when defending (if you don't take damage you don't lose tough). Unflappable and Iron Will can both keep cards flowing.

The main card in the deck however is Mutant Protectors. By it self this card is alright, often being a discard, Mutant Protectors, and a mutant, just to get a block then the minion dies. However you do get the response when they enter play effects which can be good.

This card combos well with Danger Room. Then when Mutant Protectors puts a mutant into play, you can use Danger Room to get Protective Training from anywhere onto the mutant giving them +3 health, vastly improving the chances they survive the block and giving you a buffed ally for 1 energy.

Forge can fetch Danger Room, or Cerebrowhich can help ensure you always have a mutant in hand. Changing to Piotr to fire up Cerebro can be safe if you have Armor Up in hand as well, since you can switch back to Colossus forcing an attack so you can cast Mutant Protectors.

Nightcrawler also has some extra synergy since he can bounce back into hand preventing damage, letting you keep tough up, and putting him back in hand for Mutant Protectors again, and when Mutant Protectors drops him back to the board to block, nabbing +3 health from Protective Training for free can mean he sticks around for your next turn.

The deck also has some decent synergy with Colossus' 15 cards, helping him keep Tough up, so he can cast Steel Fist, which is a very good card.