Solid card that can synergize with a lot of hero decks like Thor and Asgard trait or Avenger Leadership decks. It's a cheaper Helicarrier but more limited with the trait restriction. It can still be used in multiplayer with a call for action from another player. Also, you're not limited to a "Max 1 per player" restriction and can play up to three if you want. This doesn't stack with multiple copies to pay for the same single card.
Held Aktion: Erschöpfe Teambuilding-Maßnahme → spiele eine Karte von deiner Hand, die ein Merkmal mit deinem Helden gemeinsam hat, und senke ihre Ressourcenkosten um 1.
This card came in the Ant-man pack, and honestly Ant-man is probably where it's best. Since he's an Avenger, as well as either Tiny or Giant, Team-Building has almost infinite targets, especially if you go the Leadership route with Avengers. Almost all his cards have either Tiny, Giant, or Avenger keywords, so it's really only the tech items that don't get a discount. With Avengers Leadership, you have a slew of Avengers you can play, as well as Avenger support cards, such as the Tower, Mansion, and the Quincarrier. I've been including 2 of them in order to see one early but not have too may dead cards, and it fires basically every turn. I'm hoping more Gamma cards come out so Hulk can get the same kinda love.
At a net cost of 3 (card plus 2 resources), it will take a long time for Team-Building Exercise (TBE) to pay off. It's not until your fourth use that you're coming out ahead. How many cards in your deck match traits with your hero? Are you going to have one of those cards in your hand every turn, and will you always want to play those cards when you do have them? For most characters, the only options for matching cards will be allies, or maybe some other long-term value supports like Avengers Mansion. And while allies are great, the average deck is not going to be playing enough of them often enough to warrant TBE if that's all you have.
That said, a few heroes do have enough cards that can merit TBE. Thor and Valkyrie have Asgard cards they'll want to play out, though note that TBE and The Bifrost are not a combo. Ant-Man has Giant and Tiny cards to play,
and Wasp's Rapid Growth is a great card you'll be happy to get a discount on(see comments below, re: Rapid Growth). The Aerial events from Star Lord's pack (Dive Bomb, Agile Flight, Ever Vigilant, and Air Supremacy) could work for some heroes, but remember that it could take a while to get airborne. Whichever hero you pick, make sure your ally base supports TBE.
- Quinjet is awkward in that it is itself an Avenger you can play with TBE, but both Quinjet and TBE want to be the one playing cards out of your hand, so they're anti-synergetic in that regard. Bonus: if you're not the first player, use TBE on the first player's turn to slap Quinjet into play and start getting counters a turn sooner!
- Hellcat can act twice per turn for two resources plus your TBE. That's already pretty good value just for thwarting, but gets extra spicy with Boot Camp and/or Mighty Avengers.
- Starhawk, Red Dagger, and Hawkeye's Mockingbird can also potentially be replayed frequently for big value, similar to Hellcat
P.S. probably don't put three TBE in your deck, and probably don't put two of them on the table at the same time. It's very unlikely that you'll be able to consistently have two cards in hand that match your hero, so it'll take even longer for your second TBE to pay off than the first.