Shadowcat Can Take a Hit

You know what happens when Shadowcat defends in Phased form? Nothing, she can't take damage. What's the best way to exploit that? Try to be in Phased form and defending any time she would take damage. To pull that off you need a lot of Defense event cards with the Defense keyword that don't trigger off of you already being the defender. Things like Never Back Down and Desperate Defense are out. You don't care about boosting your defense stat afterall. In are Defiance, Powerful Punch, Jump Flip, and Side Step. These cards are intended to mitigate things when you take damage. Which they will do by making you the defender and therefore immune to damage. When you're not in Phased form to start, they'll do their regular effect, mitigating your damage, and then flipping you into Phased form. Defiance and Powerful Punch can further be used to make Shadowcat the defender without needing to exhaust.

To really make this build feel like an exploit, we have Flow Like Water, Dauntless, and Electrostatic Armor. Any time she defense with one of her event cards, she's dishing three damage back out to her attacker. Those don't need to exhaust so if you can defend multiple times, you get to dish that damage back multiple times.

The biggest weakness of this build will be getting all of your upgrades into play. You're geared around blowing your load during the Villains phase, which leaves you very few cards to play on your turn. Until you get some of the resource generating cards out (X-Jet, Unflappable, Nerves of Steel) you're paying with cards in hand. If you're not careful you could get into a loop where you're not building up your kit and not defending very well.