Cerebrawl is a 2v2, four-player fighting game that builds on the established tag-team system by letting players control both roles. It's currently on Kickstarter (opens in new tab), with developer Zero Dimension (opens in new tab) asking for $278,000 to bring it to life. At the time of writing, its campaign has earned $14,576 and will run for another 32 days.
Chiefly inspired by Marvel vs. Capcom and Street Fighter 3: Third Strike (with at least a hint of Skullgirls), Cerebrawl is all about working together with your partner. There are 1v1 fights (and 1v2s if you're feeling especially competitive), but 2v2 is the main attraction because that's where most of the unique moves lie.
There's a staggering variety of assists, cancels, and combo extenders that rely on well-timed attacks and careful resource management from both the "point" (active) player and the "benched" (secondary) player. The benched player can jump in for a quick jab, for example, an entire combo or a finisher. The active player can also forfeit their super to allow the benched player to use theirs. You can sample these moves and playable character Helen in the 1v1 and 2v2 demos available on Cerebrawl's Kickstarter (opens in new tab).
Although contingent on its Kickstarter's success, Cerebrawl is expected to release in early 2019.