Dim Mak Achievement in Halo: The Master Chief Collection

This Multiplayer medal is represented by a masked ninja icon and is available in Halo: Combat Evolved, Halo 2 Classic, Halo 2: Anniversary, Halo 3, and Halo 4. It is awarded to players upon killing an opponent with a melee attack from behind (not to be confused with a melee kill medal). Though this achievement can obviously be done in regular matchmaking as progress will be obtained naturally, this is best boosted with at least three players in Forge. To do that, be sure to follow the steps below:

• Enter Halo 2’s Forge through the Main Menu’s Multiplayer tab and set the map to Nebula
• Have all three players meet up on the single platform
• Enter Editor Mode and move the white respawn point to the edge of this platform
• One player will act as the “Dummy” player and kill themselves by jumping off the platform
• Player “A” will stand to “Dummy’s” side and melee him as soon as he spawns
• Player “B” will then beat down “Dummy” in the back, causing Dummy to fall off the platform
• This will give Player “B” a Beat Down medal and Player “A” will receive an Assist medal for the "Nice Work Dawg" achievement
• ”Dummy” will respawn at the edge right away
• Repeat this process for as long as necessary

As a note, make sure to tweak the gameplay options in the Forge lobby under “Options” before loading up the match. Under “Respawn Time,” change it to “Instant.” This will allow the “Dummy” player to respawn as soon as they are killed, giving Players “B” all 250 Beat Down medals about ten minutes or so. Once you have obtained the 250 Beat Down medals, this achievement will unlock.