Matter

Matter is an environmental element in Super Mario Galaxy. In the Ghostly Galaxy and Matter Splatter Galaxy, matter functions like a spotlight that makes platforms and terrain manifest in the space it occupies. When the matter shifts through space, the terrain disappears behind it. If Mario (or Luigi) does not keep up, he will fall through the empty space below and lose a life. There are parts of these galaxies where matter appears as bouncing droplets that briefly make terrain appear in the spots they strike. A hazard called dark matter appears in Super Mario Galaxy too, but their attributes are not related.

A similar concept is incorporated into Haunty Halls Galaxy and Sweet Mystery Galaxy in Super Mario Galaxy 2, where some platforms appear only under the shine of Bulb Yoshi's light. The enemy Mattermouth inverts this concept by eating through terrain and leaving empty space in its wake.