It first appeared in "Monster Drill". Hannibal McFist tries to control this contraption on his own, considering Viceroy is taking his vacation at that time. However, upon realizing he cannot control it on his own, he gives Viceroy some extra vacation time if he will help him control the Slaying Mantis correctly. When it first appears at the school, the students think it was the practice monster, but soon realize it's a real robot that's intent on destroying the school. Fortunately for the students (and unfortunately for McFist and Viceroy), the Slaying Mantis is no match for Randy's Ninja Air Fist.
In "Raiders of the Last Nomicon" two more make an appearance trying to stop the Ninja from escaping. They are both destroyed.
It also made an appearance in Fudge Factory, as one of the WND's trying to destroy the ninja, but was quickly destroyed.
- The Slaying Mantis also appears in the theme song.
- It is a wordplay on Praying Mantis.