Role in the Subspace Emissary
Marth, Ike, and Meta Knight were the first to spot Galleom as he was traveling through the desert in his tank form. The trio quickly caught up to him and defeated him, knocking him down onto unstable ground which gave way, and Galleom landed in the Ruined Hall, where Lucas and the Pokemon Trainer challenge him. They manage to defeat him, and, in a last desperate attempt, Galleom grabs both Lucas and the Pokemon Trainer, starts the the countdown on his emergency Subspace Bomb, then jets into the sky. Lucas manages to free both himself and the Pokemon Trainer by using PK Thunder, but in the process causes them both to fall a great distance. Meta Knight manages to catch the duo just before they land, then fly them away from the Subspace Bomb's blast. Galleom is then sucked into the Great Maze, where he is fought and defeated again by the heroes and villains (who have joined the heroes in order to stop and defeat Tabuu).
Galleom appears to be a giant, purple robot/cyborg which consists of simian features, and is also capable of transforming into a jet propelled tank labeled as the Galleom Tank. He is covered head to toe in a heavy Mech arsenal, possessing two rocket launchers as shoulder weapons, and powerful jets on his feet. He wears an iron knight mask that covers his face, as well as metallic arm braces over his bulky forearms. He is also quite agile in this form, capable of performing extremely large jumps, leading to the possibility that his jumps are jet propelled. In his tank form, he is much more compact, only being able to attack by either firing the missiles on his back, or simply by ramming into his foe at a high speed. As a last resort, he can set off a Subspace Bomb hidden within his head.