Avengers Assemble!

Easily one of the most iconic lines in the entire Marvel Universe, and one that describes the philosophy behind this deck. It's a pretty simple deck to pilot, and it's easy to strip down to accomodate to a smaller collection (Core, Captain America, RotS and MTS; anything else is just bonus).

So how does it work?

Play allies, keep allies on the table, attack with allies, win. Isn't that the way all leadership decks work? Well, kind of. But this one does a couple of specific things that are worth looking into.

Strategy

The deck works in two phases.

Building phase

During the first one, you're going to be building your economy and board so you have a decent amount of allies in front of you. Prioritize any cards that accelerate your economy (Super-Soldier Serum, Helicarrier, Avengers Mansion...) and team buffs (Mighty Avengers, Team Training). During this phase, your allies are disposable. Use them as you normally would to deal with minions, threat or blocking. You can make an exception for particularly strong allies like Goliath if you want. Cap has good defensive capabilities, so you can always take it slow, allow him to block for your allies, and build your board.

Game closing

The second phase involves you having a strong economy and 3 or 4 allies on the board ideally. Here's where the deck's tribal nature comes into play. All allies in the deck have the Avenger trait, which multiplies the power of Avengers Assemble!. Starting the turn with Lead from the Front, attacking with all your allies plus captain america, then playing Avengers Assemble! to ready everyone and attack again can pull off some impressive numbers. Make proper use of Goliath to ensure that you'll deal a minimum of 11 damage just from him in a single turn, then Rapid Response him back onto the table for even more damage.

Other considerations

Kaluu can help you get Avengers Assemble! to your hand and is a cheap blocker. The humble Stinger becomes a 6+ damage monster once all the buffs are in place, and doesn't count against your ally limit (allowing a theoretical maximum of 6 allies on the table at once). U.S. Agent is there for blocking, as he's quite cheap for what he does, though he can add some damage or thwart in a pinch. The rest of the allies are self-explanatory.

Solo or multiplayer?

¿Por qué no los dos? You can play this deck in solo with ease. In multiplayer, it can destroy even the toughest villains. Cap is a really strong hero, and this deck can buff other players if needed, accelerate them with Steve Rogers's Living Legend, Helicarrier and Avengers Tower.

43 cards? Really?

The usual caveat. Yes, really. It's not a huge difference in efficiency (though 43 really is pushing it as far as I'm concerned. I wouldn't mind going lower), given that a you have a lot of supports and upgrades in your deck, which will thin it down considerably after one pass. Still, if it bothers you, the main candidates for removal are Endurance, Team-Building Exercise and U.S. Agent

So there you go. It's not a very original deck (I'm sure there are lots of decks based on these same synergies), but it's powerful, and what's most important, a lot of fun to play.