Metalun appears to be a silvery metal creature, about twice Kirby's size, that is shaped like a dodecahedron. It has two small, black eyes on one face of its body, but no torso, ears, nose, or visible mouth. It also has two blocky feet which it tucks in as it rolls.
When a Metalun notices Kirby, its only form of attack is to pursue Kirby as far as possible and to ram into him. However, because of its polyhedral shape, it is forced to roll after Kirby one step at a time, and as a result, chases him very slowly. Occasionally, if Kirby jumps over Metalun while it is rolling, it will not notice that Kirby is now behind it, and will take a few seconds to turn around. If a Metalun reaches a ledge, it will fall off and continue rolling. However, if it hits a wall, it will turn around and roll away.
Metalun's name is derived from "metallum," the Latin word for "metal."