If your DLC won't load, check the region. A common mistake is buying the physical US cartridge and downloading DLC from a European account. The DLC has a different Title ID suffix and will not unlock.
Luigi's Mansion 3 features a robust multiplayer mode, allowing up to four players to join forces and explore the haunted hotel together. This cooperative gameplay experience encourages teamwork, communication, and strategy, adding a new layer of replay value to the game. Players can work together to capture ghosts, solve puzzles, and uncover hidden secrets, creating a fun and social experience. Luigi-s Mansion 3 -0100DCA0064A6800--v327680--US...
If your game cart is from the US, the update file must also be US region, which this string confirms. If your DLC won't load, check the region