Mecha Ridley


 * For the cybernetically enhanced version of Ridley seen in Metroid Prime and Metroid Prime 3: Corruption, see Meta Ridley and/or Omega Ridley

Ridley Robot is an incomplete robotic version of Ridley that was built by him, and is the final boss in Metroid: Zero Mission.

Battle
To defeat Ridley Robot, Samus must fire Missiles or Super Missiles at a small, glass-encased panel on his chest, which resembles the weak spot of Meta-Ridley. Only missiles will damage it; Beam weapons have no effect. It attacks by launching fireballs, homing missiles and laser beams, along with a claw swipe. Noticeably the Robot moves its head depending on Samus' position in an attempt to block her attacks. If Samus collects all 100% of the hidden items prior to arrival, Ridley Robot's offensive and defensive power will triple, making for a longer and more difficult battle than normal. Once defeated, Ridley Robot will shut down and cause the Mothership's self-destruct countdown to begin, leaving Samus with only 3 minutes to escape the ship.

Because Beam attacks have no effect and missiles are limited, the only way to regain them is by shooting down Ridley's own projectile missiles.

Interview
"At the very end of the second part, why does a robot similar to Ridley appear? Was the Ridley defeated on Zebes revived by the power of Planet Zebes's science?"

Yoshio Sakamoto: "Ridley made an image of himself to demonstrate his power by making that image as a powerful weapon. Incidentally, it is currently incomplete, and is currently at the halfway stage, becoming more massive once the walking unit and flying unit is installed." 

Trivia

 * When Samus first enters the Space Pirate Mothership, a short cut-scene of Ridley Robot's eye opening is seen, signifying that it knew exactly when Samus entered the complex.
 * The robot may be a prototype/precursor to the resurrected Ridley who is seen in the Metroid Prime games: Meta-Ridley. The fact that both of them share the same weakness supports this theory.
 * Concept art from the Prime trilogy shows a massive mechanized Ridley with wings and an apparent pilot; this may be what Sakamoto alluded to, though it was never implemented in a game.