Flippin' Tough

This is a pretty straightforward deck that just lets Colossus make the most of his kit. You want to be flipping between Hero and Alter-Ego most turns, which allows you to make excellent use of the various X-Men supports and generates tough statuses.

You want to try to get a few supports out quickly, which is not too difficult as many only cost 1 or 2. As always, Iron Will is a priority, so you have Weapon X and Piotr's Studio that can help to find it. With just those two in play that effectively gives you 8 cards when starting a turn in Alter-Ego. This only increases later further into the game once you can add The X-Jet and Avengers Mansion.

The general plan is to then alternate Alter-Ego and Hero turns. When starting in Alter-Ego, use your supports then flip. Ideally you want Bulletproof Protector to gain a second tough status. Don't be afraid to spend a tough for Steel Fist or Made of Rage, but do save 1 if you can. With the amount of card draw available you should be able to deal plenty of damage.

Turns starting in hero should be used to make it safe to flip to Alter-Ego; confuse the villain and clear some threat. Armor Up is useful for this too, particularly early on in the game. It is often worth keeping in hand, as it means starting the next turn with more cards. Try to spend all of your tough statuses before flipping.

The other nice part is that with Heroic Intuition, Iron Will, and Titanium Muscles it gives Colossus a 3-3 stat line. Therefore, Limitless Stamina is a great tool for both thwarting and attacking. To round out thwarting there is Lay Down the Law, which is super cheap and easy to play given how often you change form.

I built this in Justice as thwart is something Colossus struggles with, but as you can see the core of the deck is all basic. The same base could perhaps work in other aspects. For example, in multiplayer you could swap Justice for Aggression and go for higher damage output with Surprise Attack and Combat Training.

Update:

I haven't tested it yet, but Build Support and Superpower Training could be good here. Having more consistent access to Iron Will should be useful. If not playing NeXt Evolution the basic Hope Summers ally is perfect here as most of Colossus' events and Limitless Stamina are Superpowers. She can also search for Iron Will or Titanium Muscles! I would drop Bishop, had been thinking of replacing him anyway.