The update live now for Super Monday Night Combat introduces Steam Trading (among other upgrades and fixes), which means you can pickup crossover costume items in both this title and Team Fortress 2 for the super low price of nothing.
Four items kick off the "Friendship is Sharing" campaign for Uber Entertainment, two for each game. You unlock the hats and uniforms by reaching certain levels in Super Monday Night Combat. Here is the lowdown.
• The Gunslinger Hat, worn by Sniper in TF2, is unlocked when you get Agent Level 5 in SMNC.
• The Engineer Uniform, worn by Combatgirl in SMNC is yours when you get Agent Level 10.
• The Soldier Uniform and Rocket Launcher is Megabeth's in SMNC once you get Agent Level 15.
• Finally, Pyro will get the Assassin Helmet if you can reach Agent Level 20.
More details, plus full update notes, at the link.
Rule Changes: 5 - 5/10/12 [SMNC Forums]