Sentinels of the Multiverse
Sentinels of the Multiverse is, according to the creators, "the World's Greatest Cooperative, Comic-Book Based, Fixed-Deck Card Game." Fortunately, it is also a badass card game on its own merits.
Born when Christopher Badell got tired of every damn superhero game being either a lame exercise in "my childhood icon could beat up your childhood icon" or another damn Parker Bros. reskin, in Sentinels you play a group of superheroes (scientifically, the correct plural is a "crossover") working to fight a villain in a place.
From such simple things spring great ones.
Every hero plays completely differently, every villain has a different ballgame for wrecking your shit, and every environment has different effects on the ongoing struggle. And the lore is actually pretty amazing for the kind of thing that can be easily skipped, both because there's a few strong creative forces undergirding all of it and because it doesn't have to make everything the same forever. Hell, the art's pretty good too.
Notably, "promo" versions of different heroes with alternate powers but using the same decks are available.
Anatomy of a Turn
The villain goes first, playing the top card from its deck, then resolving all effects. This usually takes a good deal longer than it sounds.
The heroes take turns going in a set order. Each one may play a card from their hand, use a power, and draw a card in that order. If they don't play a card or use a power, they may draw two. Sometimes it's really that simple. Sometimes (lookin' at you Omnitron-X), this takes for-bloody ever.
The environment goes last, plays a card, and resolves all effects.
Repeat until the heroes or the villain get a victory, usually but not always by smashing the other into paste.
There are no limits on hand size, and when you run out of deck you just shuffle your trash and flip it over.
Notably, the villain and environment turns are completely automated, so you don't need someone to play them. In practice, however, both can get pretty lengthy and complex, so it's not uncommon to have a kind of quasi-Gamemaster run these turns for you. Additionally, the game supports between three and five heroes, with the villains scaling to match them, though players can choose to run multiple heroes. You can even play all by yourself if you're desperately, desperately lonely, and/or bought the digital version.
Heroes
Absolute Zero
Style-wise, he's kind of like Mr. Freeze, though personality and backstory-wise, he's got more in common with the later Ant-man. A depressed janitor who had the bad luck to work at Pike Cryogenics, Ryan Frost got mutated in an explosion that left him super-cold. Now he's got to superhero for the government to work off the cost of the special thermodynamic suit that's keeping him alive.
He's got a well-earned reputation as one of the most-complex heroes in the game, and for good reason: his base power involves punching himself in the balls with a fist made of either ice or fire, and half his cards do the same. What makes him tick is his equipment, which can make ice heal him and fire damage to him deal ice damage to enemies. Understandably, this puts him in something of a bind against equipment-wrecking assholes and means he may accidentally self-destruct if his player isn't good at math, but, fortunately, half his deck involves either replacing lost equipment or boosting/mitigating the effect of damaging himself. And that's not counting how nice damage boosts are on him. Not for the faint of heart or the inexperienced, but can hit harder than almost any hero in the game in the right hands.
Variants
Elemental Wrath: From the Iron Legacy timeline, where he was one of the few survivors of the titular tyrant's rampage. He's got a much-more straightforward power: punching something in the balls with cold damage.
Termi-Nation: After fighting the tech-absorbing villain Chokepoint, Zero's going in with a lot less suit. His base power boosts all damage he deal and receives by two, which makes him incredibly fragile but amazingly deadly. Handle with care.
The Argent Adept
...Well, he's a superhero bard. The latest heir to the title of "Virtuoso of the Void," Anthony Drake found that he was destined to fight the avatar of elemental chaos, Akash'bhuta, when he handled an ancient musical instrument. Unfortunately, Akash'bhuta had managed to delay the process of passing down the musical knowledge of ages to him, and he's working to make up for lost time. The superhero team known as the Prime Wardens was originally formed to help him fight her despite his being very green.
The Argent Adept is also a really complex hero to play, though not because he's in danger of self-destructing like Zero. Rather, his deck has three major components: music cards (subdivided Rhythm, Harmony, and Melody) that each have Perform and Accompany components, musical instruments that each activate two of those sub-components for different types of music card, and, of course, search cards to help get what he wants into play. If you haven't got a good head for all these kinds of things, he's really tough to play, but done right he's an unstoppable hurricane of combo-buffing. His normal power only activates a single Perform component.
Variants
Prime Wardens: Considering the team formed to help him, he'd better be a member. His new power lets him play the card on the bottom of his deck and use an Accompany text, which is... well, it's pretty nice, even if Accompany components tend to be less-direct than Perform ones.
Kvothe Six String: ...Well, the character of the Argent Adept was originally developed as a direct reference to The King-Killer Chronicles, and Rothfuss turned out to be a big fan. His new power reveals the top cards of two decks, putting one into play and the other into the trash. Most useful when villains don't want cards in the trash, obviously, but still really good for set-up heavy heroes. Unfortunately, this also means he can't activate his music without instruments anymore, making him very draw-dependent compared to his counterparts.
Bunker
The next generation of metal-suited military heroes going back to the second World War, and thus aping War Machine. A former mechanic's kid from Vegas, Lt. Tyler Vance was a decorated combat vet who was given the chance to be the next incarnation of Bunker. He became the second member of the Freedom Five, and Legacy's strong right hand in running them.
Bunker is one of the first equipment-heavy superheroes in the game, and it shows. He can equip self-repair systems, armor plating, and a variety of powerful heavy weapons, but his unique mechanic involves shifting between three Modes: Recharge mode, in which he gives up every other part of his turn to draw three cards (including the bonus for not playing or using powers) while taking less damage, Upgrade mode, in which he forgoes drawing and playing powers to get more equipment on the field at once, and Turret mode, in which BUDDABUDDABUDDABUDDABUDDABUDDABUDDA. (...Ahem, in which he gets an extra power and deals extra damage.) While these extra modes give him a unique feel, they also give him terrible turn economy, though he's still very powerful. No other equipment-heavy hero shares Bunker's toughness and ability to get extra cards. Speaking of which, his base power lets him draw a card, and one of his other cards lets him draw everytime a villain card goes in the trash.
Variants G.I. Bunker: The WWII incarnation of Bunker, who got the job because it was deemed too dangerous for a white guy, and took it because it was his one shot at promotion. He went on to kick much Nazi ass alongside his era's Legacy, fistfighting tanks and pushing the power armor to the limit, before going out in a blaze of glory trying to kill Hitler while soloing an entire fortress full of troops. His unique power, Panzer-Buster, picks an enemy and makes all damage dealt to them irreducible. Obviously, how good this is depends on how much DR is on the field, but when you do need it, it's golden.
Engine of War: Bunker was one of the casualties when Iron Legacy slaughtered the Freedom Five in his timeline. However, his former nemesis, Fright Train, was driven to repentance by his death, and joined the new Freedom Six wearing a hollowed-out, jury-rigged version of the Bunker suit. (Also, making the War Machine copy black again.) His new power discards a mode card to destroy an ongoing, something the original couldn't do at all and a priceless trick against Iron Legacy. Not a bad way to give up the bloated hand full of modes you weren't going to use soon.
Termi-Nation: The current Bunker riding in a mech after his old suit got Chokepoint'd. He can destroy one of his own ongoing or equipment card to give himself what a whole new turns' worth of actions, which can be positively badass if you know what you're doing.