Ridley Robot, also known as Mecha Ridley, is an unfinished robot build by Ridley, made to look identical to its creator, serving as the final boss of Metroid: Zero Mission.
Mecha Ridley resembles a gray, metallic version of its creator, with gray eyes and a red core on its chest, the latter of which is also its weak spot. Because it lacks legs and wings, Mecha Ridley moves about by crawling on its arms. In the place of its missing appendages are multiple cables attached to an unseen interface, giving it either power, control over the mothership, or both.
At the end of her long quest through the Chozodia temple and the Space Pirate Mothership, Samus stumbles upon a supposedly deactivated Mecha Ridley. However, suddenly, all exits to the room are locked and Mecha Ridley springs to life, triggering a conflict between the two and the final boss battle of the game. Through the heavy weaponry of missiles and super missiles, Samus eventually defeats and destroys Mecha Ridley. However, as a last resort, the machine tries to take Samus with it by setting a self-destruction timer (7, 5, or 3 minutes depending on the difficulty level) for the Mothership and locks all exits out of the ship, but Samus flees in a Space Pirate ship just in time.
- According to Yoshio Sakamoto, Ridley built Mecha Ridley to demonstrate his power as an even more powerful robotic weapon, though it was left in an incomplete state due to the Space Pirates' infiltration onto the planet Zebes to stop Samus.
- Mecha Ridley's health and strength depends on the player's percentage of collecting the hidden items prior to the fight. If Samus fights Mecha Ridley with every hidden item located in the game, Mecha Ridley's powers will triple, making the battle longer and more dangerous.