From the Super Mario Wiki
Grey Gearmo redirects here, for information about any other Grey Gearmo, see here.
“AWWW... So cute! Thanks!”
The Silver Gearmo is a minor character in Super Mario Galaxy 2. It looks similar to the Gold Gearmo. Its body and gear are silver, like the Gold Gearmo's is gold. Like its golden-clad counterpart, it wanted the player to lead an enemy into its small pen (indicated by four pegs sticking out of the ground, making a small square) once it invited them into Space Storm Galaxy. However, instead of a Goomba, it wanted a red Topman. Fortunately, there were unlimited Topmen around the area. Mario or Luigi needed to get a Topman to chase him from the start of the planet to the Gearmo, avoiding the holes in the planet and being careful not to knock him into one with a spin, while avoiding the smaller yellow Topmen that can knock the character into a hole himself.
When the Topman is in the pegs, the character would be rewarded with a Power Star for their efforts, as promised. The Gearmo would then appear on Starship Mario, sipping tea with its counterpart with the golden sheen. When talked to, it would thank the character for their efforts and give them a 1-Up Mushroom. After that, all it would say is "I love how those red guys spin!"