The Mezzanine is the second floor of The Last Resort in Luigi's Mansion 3. Luigi can access it by climbing the stairs in the Grand Lobby after he obtains the Poltergust G-00. During this first visit, Luigi is only able to explore the west half of the Mezzanine. Inside the Ballroom, Luigi finds Professor E. Gadd trapped in a painting. In order to free him, he needs to find the Dark-Light Device, which is locked inside the Storage Room.
Luigi explores the east half after obtaining capturing Kruller at the Hotel Shops. After using the Suction Shot to remove the sign blocking the door to the east section of the hallway, Polterpup leads Luigi to the Restaurant. Upon entering, he encounters some Goobs fighting over a baguette. Luigi unsuccessfully tries to sneak past them and is forced to fight the ghosts. After capturing all of them, he can head into the Kitchen, where Chef Soulfflé's cooking is filling the room with smoke. Luigi and Gooigi must team up to suck up the smoke. This angers the chef, prompting him to attack Luigi. After capturing the chef, he will drop the elevator button that leads to the fourth floor. However, before Luigi can grab it, a mouse takes it and swallows it.
The mouse runs back to a mouse hole in the Restaurant. Luigi needs to lure it out using cheese. After beating the mouse, another one will swallow the elevator button and run off. It flees into the Entertainment Room, where it hides behind some lockers. However, when Luigi attempts to approach the lockers, he is attacked by two Oozers, this being their first appearance in the game. Once the Oozers have been captured, Luigi can use the Suction Shot to break the lockers and flush out the mouse, which runs away again. This time it heads for the Restrooms. The door to the restroom on the left is blocked so Luigi must enter the one on the right. Removing a grate with the Suction Shot reveals a pipe that Gooigi can go through to reach the restroom on the left where the mouse is. After opening the middle stall, Gooigi finds a pile of mice on the toilet, including the one that swallowed the button. After retrieving the button, Luigi can finally bring it to the elevator and access the fourth floor. Upon doing so, Professor E. Gadd will prompt Luigi to return to the lab in order to introduce the Shopping Network and add a feature to the Poltergust G-00 that allows it to detect Boos.
Even though this floor's elevator button is not needed to access the floor, and only the Suction Shot is needed the unblock the eastern half of the floor, Luigi cannot skip going to the Hotel Shops and obtaining the elevator button there, since Chef Soulfflé will not appear until he does.