Luigi’s Mansion 3 will be getting a DLC but it will not be free. The DLC will be split into two multiplayer expansion but you will only need to buy the DLC once.
The first part of the DLC will be arriving on the 30th of April 2020 and will include three new ScreamPark minigames along with three new floor themes for the ScareScraper, six new themed ghost, and three new outfits.
As for the second pack, it will only be arriving on the 31st of July 2020 but they did not reveal what the second part will contain. The DLC will cost $10 and can be purchased from the eShop right now. It will also come with a new flashlight that will show the shape of Polterpup’s face on the surface it is pointed at.