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
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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