Star-Lord Leads the Guardians

This is the Star-Lord deck I used for the Galaxy's Most Wanted campaign. It heavily features the Guardians team, minus Gamora (who my wife played as a hero) and Drax (whose limitation versus minions was not appealing to me).

Upgrades for all allies make sure their attacks and thwarts are strong, so you're not wasting any consequential damage, and extra hit points make them last longer. There's no particular combo that this deck requires building to, just trying to consistently have options to do damage or thwart.

That being said, Groot is an excellent defender and can last an incredibly long time given extra HP and tough cards so that when he defends he can recover previously lost hit points.

Yondu is also great to build up, since his attacks have no consequential damage so if you can boost his ATK and ready him multiple times per turn, he can do a lot.

Iron man is there for the free Ally upgrades. Since Star Lord turns him into a guardian, he easily and cheaply triggers the Guardians team effect.

This deck is admittedly somewhat weak vs. Collector I, given that allies and their upgrades go out of play and stack the collection, so you have to be very careful in that scenario, but we did get past it by carefully keeping allies alive and not using them as often as I normally would.

We did extremely well vs. Nebula, although we might have gotten lucky card draws.

Versus Ronan... well, Ronan sucks. We were able to consistently clear all the threat on his starting schemes (yes even in the standard campaign as written) but too many times we were 1-shot with ridiculous attacks multiple times in a row, so we quit and never actually beat him.

This deck was paired with this Gamora deck for the campaign: https://marvelcdb.com/decklist/view/29543/gamora-gmw-campaign-1.0