"Mortal Kombat 11’s Towers of Time mode features various themed challenges, such as having enemy attacks coming in from offscreen, fights themed around a certain motif, and more. Some towers and fights, however, will harken back to a feature that last appeared in 2011’s Mortal Kombat reboot: Tag-team battles.
Before you get too excited, NetherRealm confirmed the feature won’t return as a standard mode. However, some towers in Towers of Time will be themed around tag battles (designer Derek Kirtzic mentions a “Shaolin Monks” theme as an example). In these towers, you play as two characters you can swap between using the right stick. The swap is quick enough to let you pull off two-character strings, too, which could make it a fun avenue for players who like to put elaborate, unconventional combos together.
There are also group battles, similar to Injustice 2’s guild boss battles (NetherRealm also confirmed there won’t be factions or clans this time around). In these fights, two players take turns fighting a powerful boss, though the player who isn’t actively on the field can help their friend throwing out assist attacks. You can also take on these bosses as a tag team, swapping in and out on the fly.
Tower of Time also has a form of competitive co-op with leaderboards. At the end of each tower, you’re given a few rewards and a score. At the end of the week, you will earn bonus gear and items depending on how well you did across all towers versus the rest of the playerbase, which offers an incentive to keep coming back and earn high scores."
Read more at https://www.gameinformer.com/2019/04/02/mortal-kombat-11-has-limited-tag-team-battles-in-single-player