Four decks split between Heroes and Villains, built on team attacks, +1/+1 counters, connive and a four color spellslinger.
Teamwork N is an optional additional cost: tap any number of your creatures with total power N or more as you cast the spell. It turns a wide board into a discount, and it costs you the attack that turn.
Counters are everywhere in this set, and the Jeskai Hero deck in particular treats them as its main resource rather than a side effect.
Connive draws a card, then makes you discard one, and puts a +1/+1 counter on the creature if you pitched a nonland card. The Grixis Villains deck uses it as both filtering and growth.
Battalion triggers when a creature attacks alongside at least two others. It fits a set where the flavor is a team charging in together.
Marvel's Super Heroes is the crossover with the widest cast so far, and the four decks split cleanly into Heroes and Villains. The mechanics follow that: teamwork asks your creatures to work together to pay for a spell, battalion pays out for attacking as a group, and connive gives the Villains their card selection.
Counters do the heavy lifting across the whole product. If you like a board that gets bigger every turn rather than one that combos off, this set is aimed at you.
Avengers Assemble is the most straightforward and the best first deck. The Fantastic Four is the most demanding, both on the mana base and on remembering to cast a noncreature spell every single turn.
Captain America, Team Leader · Director Nick Fury
A Jeskai Hero typal deck from Marvel's Super Heroes that piles +1/+1 counters across the whole roster. Captain America, Team Leader hands every Hero vigilance and haste the turn it lands and stacks counters on the team, while Director Nick Fury discounts your Heroes and digs for more.
Doctor Doom, King of Latveria · Loki, the Deceiver
A Grixis Villains deck built on connive, discard, and life drain. Doctor Doom, King of Latveria punishes opponents every time you pitch a land and hands out connive triggers, while Loki, the Deceiver copies your Villains for extra attackers and card draw.
Mister Fantastic · Invisible Woman
A four-color spellslinger deck built around casting a noncreature spell every turn to switch on the whole team. Mister Fantastic draws cards and copies your best triggered ability, and Invisible Woman walls up the board before turning your creatures unblockable.
T'Challa, the Black Panther · Shuri, the Black Panther
A Selesnya artifacts deck that churns out indestructible Vibranium tokens and rewards big artifact casts. T'Challa, the Black Panther banks Vibranium and grows on every four-mana artifact, while Shuri, the Black Panther turns a wide artifact count into card draw and a team pump.