|First Appearance||Halloween Spectacular of Spooky Doom|
The Nightmare Mech was a robotic, bipedal walker that was either built or found by Zim in the Nightmare version of Professor Membrane's lab. He used it to rescue Dib from Nightmare Bitters' clutches and escape from the Nightmare Skool. It was then set on autopilot to provide cover fire for the two unlikely allies as they made their escape; it was demolished by Nightmare Bitters shortly afterward.
The walker moved on two powerful legs, and its skull-shaped cockpit was entered through its open "mouth." It was capable of bounding across a great distance in a short period of time, and was also armed with hoses that squirted some kind of green fluid. This fluid, however, does not seem to have any effect on targets aside from eliciting disgust.
It also had an autopilot function, whch proved handy when Zim and Dib were trying to find a way to open the portal in the latter's cranium.