Overwatch's got a whole new mode for players to try out: 6v6 Lockout Elimination. This new arcade mode went live at the conclusion of the Overwatch Anniversary event and it's pretty damn fun.
For those that haven't tried out Lockout Elimination in the custom game browser, the mode works like this: players select their heroes and play a round as normal. But once you die with a hero, they aren't able to be used for the rest of the match. The first team to lose three rounds loses the match.
As you can see, these matches are played on the Arena maps, which include Ecopoint Antarctica, Necropolis, Black Forest and, Castillo.
This means 12 players are running around on maps meant for six. Not only does this lead to some extremely close quarters matches, but it also makes champions with area of effect ultimates very useful, like Reaper or Pharah.
Of course, as Jeff Kaplan notes, you'll want to be careful running too many healers early on in a match, because if you do, you run the risk of losing them all too early and being extremely squishy later in the match. This is especially true as health packs are non-existant on the map. DPS with an off-heal ability like Soldier: 76 are therefore going to be invaluable.
It's important to note that you could technically already set up these matches through the Custom Game browser, but the new mode awards loot boxes as it is classified as Arcade for the time being.