Halo 5: Guardians' newest multiplayer is Warzone Firefight, and 343 Industries showed it off in this trailer released yesterday during the Halo World Championship Finals.
As the name suggests, this mode is a combination of Warzone from Halo 5 and Firefight, a very popular mode from 2009's Halo 3: ODST. In it, teams of up to eight human players work cooperatively against enemy AI in over five rounds of increasingly difficult objectives, according to this post on Xbox Wire.
Halo 5 multiplayer's REQ system is available in Warzone Firefight (as it is in Warzone) to aid in repelling the oncoming threat, which 343 says will feature "the most on-screen enemies in the history of the franchise." In addition to the standard class of enemies, Warzone Firefight will also introduce "Mythic" class bosses to toughen the challenge even more.
Warzone Firefight comes to Halo 5: Guardians sometime this summer.