The Brain Robot is the third boss in Metal Slug 6.
The Brain Robot is a large robot controlled by an artificial brain. The brain is housed inside a glass dome in order to protect and preserve it. It also has eyes, connected to the brain through nerves. This may imply that the eyes previously belonged to the same creature as the brain.
Its appearance may look sorrowful, as it wanders around alone in the sewers of the 3rd mission.
The entire fight resembles Huge Hermit's, which means you have to run away from it while trying to shoot it. It can use its brainpower to send electric balls homing in towards you. Sometimes, it will take a truck (sometimes a car or a bus), and tries to throw it at you. When you get too close to the Brain Robot, it will attack you with its mechanical claws. After getting too close to the Brain Robot 5 times, the Brain Robot will repeatedly stomp the ground before it sends an electric current through the water at its feet to electrocute the player. At times, when throwing the truck, it can send a swift array of electric balls that go in a wavy direction. If you have a Zantetsu Sword, attacking the balls can get you coins if you have your meter on MAX.
Invaders: The original model built by the Invaders.
Martians: The Martian's take on the Invaders' model, it was built by the Professor. It is stronger than the original model, possessing stronger attacks and is completely red. It appears in Metal Slug Attack.
When it uses its claw and misses too much, it will stomp angrily, and when it walks, it spreads out its arms, and walks a bit faster, making him more dangerous to get close to attack him.
- The Brain may bear a resemblance to the Final Boss of Starfox 64.
- Its walking animation also bears a resemblance to the Death Egg Robot of Sonic the Hedgehog 2.
- This is the only situation so far in which the player is given the opportunity to battle with the Proto-Slug Gunner. However, most players admit it is difficult to fight with due to the open top, leaving the player exposed and vulnerable to its many projectiles.
- In Metal Slug Defense, the Brain Robot is the second toughest unit in the game, with 50,000 HP at Level 40.
- Also, Brain Robot is the toughest unit in the Alien Faction.
- In Metal Slug Attack, the Brain Robot is available as a unit either from the Guild Shop, requires x80 parts to unlock, the robot also includes an additional (special) attack not in Metal Slug Defense, a wall of electricity that the Brain Robot performs in Metal Slug 6, used for crowd control, and very high damaging and also can damage air units.