To obtain this achievement you are required to direct impact two enemies with the Spartan Laser on the Castle DLC maps. A Castle DLC Map, Outcast, has two lasers that spawn at the start of the match. The both spawn towards the right side at the spawns. Once you've acquired the laser simply hold it down and direct impact two enemies in the same match. You can also direct impact two enemies with one laser blast and earn the achievement. The achievement will unlock immediately after killing two enemies with a direct blast netting you 20 gamerscore. Outcast is the only Castle DLC map that intially spawns Spartan Lasers but you can get Lasers from an ordnance drop on the other maps (Daybreak and Perdition) on the slayer variant game types. Spartan Lasering a Warthog with two people in it should also net you the achievement. This will also count towards destroying two vehicles as well increasing your progress with the Scrapyard achievement.