Mario's Star (item)
From the Super Mario Wiki
Mario's Star is an item of Mario that Luigi finds in Luigi's Mansion. It is found in the Observatory of the mansion, in Area 3. It is accessible after shooting the moon with a Shining Ghost, a layer of ground will appear, on the other side, there is the star. This possession, along with Mario's Glove, Mario's Hat, Mario's Letter and Mario's Shoe are scattered around the mansion. Unlike the other items, collecting this one causes the same "shining" noise from Super Mario 64 when collecting a Power Star to play. If Luigi takes them to Madame Clairvoya, she will use her crystal ball to "communicate" with Mario. After receiving the star, she says: "Wh-what is this? If it isn't Mario's Star! What otherworldly beauty!"
Mario's Star is the only Mario possession in the game whose location isn't changed in the 3DS Hidden Mansion.