Mssr Boo is the seventh boss Toad faces in the VS COM mode of the Super Nintendo Entertainment System version of Wario's Woods. However, if the player chooses the hard level difficulty, Mssr Boo will be the first boss Toad battles. The ghost is found in the vine-covered hills. His relationship with the Boo species is unknown.
Judging from his beret, "Mssr" is intended to stand for monsieur, the French word for mister; however, "M" is the correct abbreviation. In the Satellaview versions, Mssr Boo is the fifth boss Toad faces, and he is in the underground cavern instead.