From the Super Mario Wiki
“Lumalee! Lumabop! Welcome to the Luma Shop!”
—Lumalee, Super Mario Galaxy
Lumalee is a turquoise Luma who appears in Super Mario Galaxy and Super Mario Galaxy 2. She is the proprietor and sole employee of her own 'shop', where Mario can purchase either a Life Mushroom or a 1-Up Mushroom for 30 Star Bits. Lumalee can be found in several galaxies and tends to appear before boss battles. Once Mario has made his choice of purchase, Lumalee is fed the proper amount of Star Bits automatically and proceeds to transform into the mushroom of his choosing for him to collect. Because of this transformation, Mario can only buy one item from Lumalee for every time she appears, unless he restarts the level and makes his way to her again.
Official artwork of a Lumalee
with two Chance Cubes
in Super Mario Galaxy 2
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.