From the Super Mario Wiki
“Lumalee! Lumabop! Welcome to the Luma Shop!”
Lumalee is a traveling "shop" in Super Mario Galaxy and Super Mario Galaxy 2 that sells helpful items to Mario usually right before he fights a boss. It is run by a turquoise Hungry Luma who holds the items for sale on sticks. The shop only sells 1-Up Mushrooms and Life Mushrooms, each for thirty Star Bits. After Mario feeds the Star Bits to the Luma, it will transform into the item that Mario has chosen. Because it transforms after purchase, Mario can only buy one item per appearance of Lumalee.
In Super Mario Galaxy 2, by doing a certain mission, Lumalee will appear in a pipe that is at one ear on the Starship Mario. The first Lumalee will turn into a Chance Cube for 30 star bits. The second Lumalee will turn into 5 Chance Cubes for 100 Coins. The possible outcomes from both Luma Shops' Chance Cubes are a single Star Bit, a 1-Up Mushroom, three 1-Up Mushrooms, and five 1-Up Mushrooms.