Waiter

Waiters are uncommon ghosts found in Luigi's Mansion. They are light blue ghosts dressed up in waiter outfits that carry plates of food in each hand. Similar to Gold Ghosts and Greenies, Waiters only have 10 HP.

They are found in only one room of the mansion, where they serve to endlessly supply Mr. Luggs with food, posing no direct threat. However, as long as they are left alone, Mr. Luggs will continously eat, meaning that he cannot be defeated. Upon vacuuming the Waiters up with the Poltergust 3000, Mr. Luggs will no longer have food being served to him, causing the battle with him to start. Alternatively, they can be stalled by flashing them with the light (causing them to dissipate and reset) allowing Luigi to suck up the food without capturing them, after which Mr. Luggs will fly into a rage and they will flee in terror. After the boss is defeated, Waiters do not appear again for the remainder of the game.

Luigi's Mansion (Nintendo 3DS)

 * In-game description: "A ghost in the Dining Room. His hands are full, so he can't grab."

Trivia

 * Despite the fact that the Waiters' hearts are not protected by fire, water, or ice, they are unaffected by elements.

Reference
Cameriere