In the above video, Game Director Jeff Kaplan explains why Deathmatch wasn't a part of Overwatch until now. Deathmatch has a way of drastically de-prioritising both of those things. But the Arcade, said Kaplan, has "opened up our ability as developers to introduce game modes to you guys that we wouldn't normally feel comfortable putting in the Quick Play or Competitive rotation". He acknowledged that he once said deathmatch would "never" come to the game, but said the Arcade, which was added to the game late previous year, has proven to be a game-changer.
In free-for-all deathmatch, players will have to go up against seven opponents and try to get as many kills as possible while avoiding dying by seven other players. All you've gotta worry about is eliminations.
Blizzard will also be rolling out altered maps for the mode, as well as a brand new one specifically for the deathmatch modes.
It seems likely that this new build will take a while to test and will likely launch sometime after the end of the Overwatch Summer Games. The top half of players in the lobby will get win credit towards loot boxes earned in the Arcade.
Deathmatch is a free-for-all in which players must, in the grand tradition of the mode, murder each other over and over until a specific kill target is reached. Kaplan said that Mercy's Resurrect Ultimate will actually take kills off of the scoreboard from the other team, and that the three-on-three Arena maps and modified Capture the Flag maps will be available for this mode. I'll probably steer clear until Blizzard realises this idea, while interesting on paper, is extremely bad. Deathmatch modes are available on the PTR right now, and will be releasing to the live client in a couple weeks.