I'm pretty sure the answer is "I am Groot."

EDIT: Of course, you can take Iron Man as a replacement because he counts as a guardian (because of Star-Lord's ability) and all upgrades are for free

Theme of this deck is to put Groot on the table and get upgrades for him to get his health to 10 (6 basic health + 1 Comms Implant + 2 Reinforced Suit + 1 from Team Training.

Put also Clarity of Purpose at him because of his healing ability.

With Ready for Action, Groot get's a tough status card and because of his ability, he defends -> blocks with tough and heal for 2.

So the perfect round looks like this: Use Clarity of Purpose to generate a resource -> play Ready for Action to get him a tough status card -> defend with him - he take's no damage and heals for 2.

Black Panther is there to find Ready for Action, Suit Up or "Welcome Aboard". Depends on the game.

Gamora gets us an event, every time she activates

Nova Prime or Beta Ray Bill take the last spot on the roster to damage someone.

If you have "Welcome Aboard" an Suit Up in your hand, play Suit Up and get one of the ally's in your hand. Play them with the discount of Star Lord's ability and benefit from "Welcome Aboard" to discount a hero by 5.

With all this we have also Guardians of the Galaxy to draw a ton of cards while we playing upgrades on our ally's. Knowhere get's us another draw because every ally is a Guardian

Med Lab in case we lose someone to bring him back the next round

Thwarting will not be an issue because of the upgrades and of course Leader of the Guardians.

Element Gun is here to play dead cards or just for fun :)