The Bee Mushroom is one of the power-ups in Super Mario Galaxy and Super Mario Galaxy 2. The Bee Mushroom turns Mario or Luigi into Bee Mario or Bee Luigi, giving them the ability to fly until the flight gauge reaches zero, when they will descend slowly. When Mario or Luigi land on the ground, the flight gauge will fill up, and they can fly again. The Bee Mushroom also gives them the ability to climb on Honeycomb Walls.
The Bee Mushroom has appeared in Super Mario Galaxy and Super Mario Galaxy 2. This power-up is usually found in places that are forest-themed, like Honeyhive Galaxy and Honeyclimb Galaxy, but sometimes it can be found in a tropical themed galaxy like Sea Slide Galaxy. In Super Mario Galaxy 2, the Bee Mushroom comes back and helps Mario and Luigi through the galaxies in the game.
The Bee Mushroom, like all the other power-ups, has several ways to revert Mario and Luigi back to normal. The more obvious way is to take damage, and another way is to touch water to revert Mario back to normal.