If you found yourself watching gameplay videos of Luigi’s Mansion 3 and were left wanting more, then you may be pleased (or not) that there will be some paid DLC in addition to the core game.
However unfortunately, that is all we know. We simply know that there will be DLC for Luigi’s Mansion 3 as there is a note about it in the game’s description on the Switch eShop.
When more information becomes available, will be sure to let everyone know.
Source: Switch eShop