Double Trouble Achievement in Halo: The Master Chief Collection

This Multiplayer medal is represented by two stars within a purple circle 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 two opponents within four seconds of each other. Like the Legendary medals achievement, and mostly of all of achievements that will follow this one, there is no definitive way to boost Double Kill medals.

You'll need to work with a coordinated team in order achieve two kills within such a short time frame. Team SWAT is one of the best playlists to work on this achievement since players are automatically stripped of their shields, thus meaning you can gain Double Kills a little easier than in a standard Team Slayer game. Once you achieve 250 Double Kill medals, this achievement will unlock.