Only seen during the Black Ops Battle on Normal or higher difficulties, the Reaper Mk-13 is a small anti-personnel drone used by the Black Ops. They will actively hunt down and reveal players, making some spots and tactics less effective, even outright worthless.
The Reaper Drones have all the same abilities of the Black Ops and come with a dangerous attack to boot. Best to kill them immediately so they cannot allow Black Ops to target gunships or fire EMPs at your position.
The best weapons to quickly dispatch the drones are those with very long range. The Barrett M112 can dispatch the flying menaces in a single shot in the right hands. The XM814 Heavy Machine Gun and M5 Pulse Rifle will also make short work of them. However if not available, the extremely common M45 Marksman Rifle will still make due, and receive a healthy damage boost from the drones status as Light Enemies.