The Luigi Mushroom closely resembles a 1-up mushroom but the base of it is also green and there is a green L on the cap of the mushroom.
When collected, the player who collected it will gain the physics of the characters in New Super Luigi U. The player will have lower traction when stopping. They player can jump higher than before and can hover in mid-air temporarily.
The only ways to lose the New Super Luigi U physics are to die or to complete the stage. All physics revert back to normal afterwards.