The item Boulder Mushroom does exist. However, it is mostly known as Rock Mushroom. You may find out more information about it by clicking here.
Boulder Mushroom
Boulder Mushroom
  • First Appearance
Luigi's Mansion 5: Curse of the Mansion (2010)
  • Latest Appearance
Luigi's Mansion 6: U Are Doomed!! (2012)

The Boulder Mushroom (also known as Rock Mushroom) is a Power-Up that first appeared in Luigi's Mansion 5: Curse of the Mansion. Should Luigi grab one, he will transform into Boulder Luigi. After being obtained, Luigi's hat will turn into hard stone as well as his overalls. The player can encase Luigi inside a boulder by pressing the 2 button on the Wii Remote. After doing so, Luigi will roll around, damaging almost anything he crashes into. If Luigi crashes into something solid, he will return to his normal state, however, he will keep the Boulder Mushroom. Like usual, the player can return to Luigi's boulder form again by pressing the 2 button on the Wii Remote. While in the boulder form, it is possible to return to the normal form by jumping and pressing the Z button when on the Wii Nunchuk. This is a helpful solution to stop Luigi from falling off an edge. This ability, however, is prohibited when completing the only level of the Bowling Boulder Mansion (Boulder Bowling Bash). This is probably because it would make the mission too obvious. This power-up plays its most important role in the Bowling Boulder Mansion, which is also its only appearance.

The Boulder Mushroom returns in Luigi's Mansion 6: U Are Doomed!!. Unlike the prequel, it is found in two mansions instead of one: the Boulder Band Mansion and the Rock Stock Mansion.