Massacre is one of the achievements obtainable in Monaco. It is awarded for killing every enemy in a mission. As of March 2015, only 25.8% of Steam users had achieved Massacre.
Bring the Bleach | Cerveau | Dem Bones | Identified | I Work Alone | Massacre | Play It Again Sam | Silent Withdrawal | Slippery | Technician | Time to Retire | Unscathed | Whacked