Blue Grass Galaxy

Blue Grass Galaxy (also formatted as Bluegrass Galaxy) is a rumored location that, starting around the early 2010s, has been claimed to be present in prerelease versions of Super Mario Galaxy 2. It is associated with footage from the game's E3 2009 reveal trailer, or an unused music track in the game's files.

Though rarely acknowledged as such during its spread, the name is derived from bluegrass, a genre of country music that features acoustic string instruments.

Within the game's soundtrack, the "Puzzle Plank Galaxy" music is most closely associated with the bluegrass genre. The rumors are sometimes attributed to this. Contrary to these claims, "Blue Grass Galaxy" is not the track's official title in the English or Japanese soundtrack, although it may have been an unofficial name that fans overinterpreted.

The files for Super Mario Galaxy 2 do include several unused music tracks, which have sometimes been labeled after Blue Grass Galaxy. However, none of them are in a country style, nor do they have very descriptive or relevant file names.