From the Super Mario Wiki
“What's that? A striped mushroom? I've never seen one of those before! You, uhh... Yeah. Have fun with your unusual toy there. I ain't judging!”
—Lubba, Super Mario Galaxy 2
The Bee Mushroom is a yellow mushroom with brown stripes on the cap which acts as a power-up in Super Mario Galaxy and its sequel, Super Mario Galaxy 2. The mushroom is first found in the Honeyhive Galaxy after collecting a ? Coin. It is also found in Super Mario Galaxy 2 in the Honeybloom Galaxy. Once Mario or Luigi collect the Power-up they will become Bee Mario or Bee Luigi and will then be able to fly for a limited time, climb honeycomb walls and cling to the Queen Bee. Bee Mario is also uniquely capable of standing on flowers and clouds. If Mario or Luigi touch water when they have on their Bee Suit, they will go back to their normal form. It also appears in the Honeyclimb Galaxy, Gold Leaf Galaxy, Sea Slide Galaxy and Sand Spiral Galaxy. In Super Mario Galaxy 2, it appears in the Honeybloom Galaxy and the Honeyhop Galaxy. Also, once Mario or Luigi gets 120 Power Stars, a Bee Mushroom will appear in the Tall Trunk Galaxy in the ending credits.