The Megadoomer is, as it's name suggests, a 'Combat Stealth Mech', likely a prototype due to the 'X-3' designation. Designed by Vortians, the only model seen was originally to be shipped to Invader Tenn on Planet Meekrob, but was instead shipped to Zim due to the 'revolutionary' actions of a rebellious slave on the Conveyor Belt Planet. It makes its only appearance in "Megadoomer", the episode.