Silver Star

Silver Stars are Stars that first appeared in Super Mario 64 DS, and returned in Super Mario Galaxy and Super Mario Galaxy 2. In all of the games that they are present, Mario (or other playable character) must collect five of these Stars in some levels to form a Power Star.

Super Mario 64 DS
Silver Stars were introduced in Super Mario 64 DS, being a new feature to the game. In some levels, the player must collect five to get a Power Star. They are found in almost every course and in Sunshine Isles. If a character gets damaged while holding one or more Silver Stars, he will lose one and it will scatter and bounce around the area nonstop. The player must catch it again to retrieve it. The touch screen shows the location of these stars.

Similar physics are used in the multiplayer mode of Super Mario 64 DS and the missions may have been the inspiration of the multiplayer mode or the other way around. However, in multiplayer, the Silver Stars are replaced by Power Stars.

Super Mario Galaxy
Silver Stars reappear in Super Mario Galaxy having the same role as in Super Mario 64 DS. This time, the player will not lose one if they manage to take damage. The Stars also float around Mario, unlike in Super Mario 64 DS where they "disappeared", after being collected.

Super Mario Galaxy 2
Silver Stars appear again in Super Mario Galaxy 2, having the same role as they did in the first game.

Trivia

 * In Super Mario Galaxy and Super Mario Galaxy 2, when a Silver Star is collected, it makes the same sound as a Luma would make. This is probably because it is a transformed Luma, but that has yet to be confirmed.