Spring (Super Mario Galaxy)
From the Super Mario Wiki
Springs are extremely rare, indestructible enemies appearing in Super Mario Galaxy. They resemble yellowish brown elipses with two beady eyes and four sprouting springs. Spring enemies move from side to side in order to bounce and delay Boo Mario, thus hindering the passage. Only four spring enemies appear in the entire game, and only in Boo's Boneyard Galaxy. The player's character cannot affect them at all.