There is a song that can be easily accessed in the sound test that never appears in-game. It resembles part of a track from its Amiga port, Turrican 3.
Contributed by MeleeWaluigi
In the game's data, there are unused sprites that appear to be Mario and Sonic frozen in carbonite in the same manner as Han Solo in Star Wars Episode V: The Empire Strikes Back. They were most likely to appear after the first mini-boss, according to screenshots previewing the game in the German magazine Amiga Games.
Contributed by CosmykTheDolfyn