The Reapers are an independent group who specialize in stealth mechanics and can be added to your squads when launching into missions. They utilize a new form of stealth called Shadow Concealment which allows them to stay hidden even after initiating an attack. They have some high powered equipment in the Vektor rifle and explosive claymores. Once a claymore has been set any soldier can activate it, and by using the Homing Mine ability, claymores can be attached to an enemy to make them walking bombs.
Reapers can choose different skills that allow them to enter shadow mode more quickly or conversely can spec out for more explosive and offensive oriented skills.