Nice job
Heh, the Vanilla Dome, Bowser Valley, and Special World overworld themes were my three favorite tunes from the game actually. Mostly because they just bring out some of the best from the game with great challenges to the player.
The xylophone sounds brilliant with the high notes. The piano playing deep notes was a nice touch here as well. The other deep sounds I hear are just icing on the cake. You did a good job of making a cover version of this song.
Overall, nice!!