Koopa Stage BGM
Koopa Stage BGM is the tune that is played when you're in the level 4 castles of each world. It is a fast-paced tune which really expresses the amount of danger and difficulty to expect in the castles. The title comes from the Famicom 20th Anniversary Original Sound Tracks Vol.1 album.
Super Mario Bros. (NES)
The song plays in double time if you have fewer than 100 seconds remaining. Both versions loop.