The Robo-Mantis is a giant robotic praying mantis created by Willem Viceroy. It's first appearance was in "Monster Drill". Hannibal McFist tried to control this contraption on his own, considering Viceroy was taking his vacation at that time. However, upon realizing he could not control it on his own, he gave Viceroy some extra vacation time if he would help him control the Robo-Mantis correctly. When it first appeared at the school, the students thought 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 Robo-Mantis was no match for Randy's Ninja Air Fist.
Several other Robo-Mantis's appeared in "Raiders of the Last Nomicon" trying to stop Randy from escaping McFist industries, Randy easily escaped them.