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Parasite Queen is the theme that plays during the battle with the boss of the same name in Metroid Prime. The theme somewhat resembles Mother Brain's theme in Super Metroid. A remix of the theme is used for the Amorbis battle in Metroid Prime 2: Echoes, and the Fire and Arctic Spawns in Metroid Prime Hunters. The latter has an unused Sound Test title, Demon Spawn, in the internal "BGMSELECTLIST.DAT" file.
The original theme appears in Super Smash Bros. Brawl on the Frigate Orpheon stage, and on Pyrosphere in Super Smash Bros. for Wii U, both times titled Vs. Parasite Queen. In the latter game, the song must be unlocked by recovering stat boots stolen by a Metroid in the Smash Tour mode. The original theme is also included on the Metroid Prime & Fusion Original Soundtracks, titled VS Parasite Queen.