The Three-Eyed Crab Alien is an alien creature from The Grim Adventure of Billy and Mandy episode, "Moon the Moon". He was one of the aliens in the mechanical tank that Billy destroyed. The Crab Alien went after Billy and they both get into a huge brawl but in the end, the Crab Alien gets spanked by the mechanical robot and defeated. Billy tooses the three aliens with one eye and throws the crab alien on them. The Crab Alien turned into a werewolf alien, with the other aliens.