Room B-4 is the fourth course of the Basement in Mario vs. Donkey Kong: Minis March Again!. It is unlocked by earning 60 silver stars or better from previous levels. The soundtrack of this course is based on the castle theme from Super Mario Bros. and was also used in Mario vs. Donkey Kong 2: March of the Minis as the soundtrack of Lava Dome.
The course features three mini toys.
The course has a symmetrical layout. The minis start next to each other in the bottom left. The Goal Door is on the other side of the course, also at the bottom. The minis have to be guided with Pink Blocks to the other side of the stage while being protected from the fireballs shot between two pairs of Piranha Plants on either side of the course. Split Pipes of various colors can be used by the minis to reach bonuses located higher in the course.
Mini Mario Card
The Mini Mario Card is located in front of the Piranha Plants at the left side of the course. The minis can reach it by entering the cyan Split Pipe at the bottom and exiting from the one at the top, then immediately falling down to collect the card. Another way of reaching the card is to bring the minis to it using Pink Blocks, maintaining a gap right under it so that the minis do not walk into the Piranha Plants.
The M-Token is located in front of the Piranha Plants at the right side of the course, symmetrically opposite from the Mini Mario Card. Much like the Mini Mario Card, the token can be obtained by using the Split Pipes on the right side of the stage from the bottom to the top, or by leading the minis to it with Pink Blocks while maintaining a gap under the token to keep the minis from walking into the Piranha Plants.