The Basement is a bonus floor in Mario vs. Donkey Kong: Minis March Again!, unlocked after the player completes the main game. On the level select screen, it is placed before Floor 1, Mini Mayhem. Each level in the Basement is unlocked by obtaining a certain amount of stars throughout the game.
The Basement contains courses that are more difficult than usual. The enemies featured on this floor are Capture Kongs, Piranha Plants, Snifits, Polterguys, and Thwomps. It also features Conveyor Belts, Magnets and the ubiquitous Pink Blocks among many other elements.
A particularity about the Basement is that most courses here have their own soundtrack, which may be either a composition from Mario vs. Donkey Kong 2: March of the Minis or a new composition. The only courses in the Basement to share the same soundtrack are Room B-4, Room B-5 and Room B-6, which use an arrangement of the castle theme from Super Mario Bros., also heard in Lava Dome in Mario vs. Donkey Kong 2: March of the Minis. However, for each of these courses, the track is looped at a different point. The music on the Basement's level selection is screen is likewise reused from Lava Dome's level selection screen.