The kill bot appears in the Co-op Missions mutator "Kill Bot Wars." The robot is invulnerable, but has a kill counter above its head. After a certain number of kills, the kill bot destroys itself. The number of kills required varies depending on what time the kill bot appears, if before 10 minutes, it takes 30 kills, but if after 10 minutes it takes 50.
There are three types of kill bot; the murder bot, death bot, and kill bot. Each type is larger than the previous, deals more damage, and takes more kills before it self-destructs.
The kill bot is also an option for Amon to receive in a gift in the mutator "Gift Exchange."
The robot is possibly named after the killbots of the Futurama series, which shut down after 999,999 kills.