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Vs. Parasite Queen (VS.パラサイトクイーン) is the theme that plays during the battle with the Parasite Queen in Metroid Prime. It consists largely of a relentless percussion line accompanying tense and dissonant chords descending chromatically. Stylistically, the theme somewhat resembles Mother Brain's theme in Super Metroid, as well as Amorbis's later theme in Metroid Prime 2: Echoes. Rythmically, it bears a slight resemblance to Quadraxis's theme.
It is available in the Soundtrack Gallery in all Wii versions of the game, where it is titled simply Parasite Queen. The original theme is also included on the Metroid Prime & Fusion Original Soundtracks.
A remix is heard as the Morph Ball theme in Metroid Prime Hunters: First Hunt. A slightly-altered version is heard when battling 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. In Adventure Mode: The Subspace Emissary, the theme serves as background music for the first part of The Research Facility (Part II). It is unlocked randomly by collecting CDs in Brawl. In Smash on Wii U, the song must be unlocked by recovering stat boots stolen by a Metroid in the Smash Tour mode.
Super Smash Bros. Ultimate features a darker, faster remix of Vs. Parasite Queen. This version was arranged by Motoi Sakuraba, best known for composing various titles in the Tales series. It is playable on any Metroid stage, and is used in the Character Showcase Video for Dark Samus. It replaces the original theme from Prime, which is the only Metroid track from a previous Smash game not to return in Ultimate.