Excluding this, achieving this medal on Social/Mythic Big Team Battle would be extremely noteworthy, because that would mean the whole team would need to be in respawn which as a team effort wouldn't be impossible. Perhaps the hardest conventional team slayer playlist to get this medal on would be Slayer, as it has a battle consisting of a four-on-four match. If any respawn before you get the overkill, you will not get the medal. In order to unlock the medal, you have to kill the entire team so fast that every member of the team is simultaneously dead for at least a moment. It is helpful to note that just getting an overkill on a four-on-four match in Matchmaking will not necessarily achieve the medal. This medal is extremely difficult to earn, as you rarely find all of the same team together, and it is hard to stay alive killing at least four enemies within four seconds of each other. It is represented by a gray cross with a red skull.

The Extermination medal is a special medal obtainable in Halo 3, Halo: Reach, Halo 4, and Halo 5: Guardians Multiplayer for killing the last alive player on the opposing team with at least an Overkill that results in the entire team being dead at once.

Halo 3 br overkill extermination'