Glass Mushroom

Glass Mushrooms make their debut in Super Mario Galaxy 3 - Neverending Galaxies. They turn Mario into Glass Mario, Glass Mario acts like Superstar Mario, being able to run through enemies. However, Glass Mario can walk over dangerous hazards, such as Dark Matter, quick sand, lava and very cold water. The only downfall is that if Glass Mario gets hit by a hammer, boomerang, ect, he will shatter, causing him to lose a life. Glass Mario can not survive Black Holes, bottemless pits, or any sorts of ways Mario/Luigi can lose a life no matter what power-up they have. Glass Mario has the ability to shatter other windows that are made out of glass. Even if Glass Mario/Luigi seems very overpowered, Glass Mushrooms are very rare, only appearing in a secret mission of Haunted Ghosts Galaxy, and Hot Hot Desert Galaxy.

Trivia:

Glass Mushrooms are the only power-ups (so far) only appearing in 2 galaxies.