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"Space Pirate encrypted data decoded."

The subject of this article is not named in-game.
The current title is from the game's internal data.

Boss Zeta,[1] also known as Boss Battle 4,[2][3] is a battle theme from Metroid: Samus Returns. It is composed by Daisuke Matsuoka.


Boss Zeta plays during encounters with Zeta Metroids. It opens with a shrill stinger, followed by a low choir reminiscent of the Chozo temple themes from Metroid Prime and Metroid: Zero Mission. The rest of the track is an exciting high-energy battle theme, with a more cinematic flair compared to Boss Alpha and Boss Gamma due to featuring an dramatic brass melody in lieu of the standard electronic synths. It can be heard here: [1]

Boss Zeta appears to be a largely original composition, not based upon any of the songs composed by Ryoji Yoshitomi for Metroid II: Return of Samus. However, the opening stinger is notably similar to the original Metroid battle theme from Return of Samus. This may have been a deliberate reference by Daisuke Matsuoka, although this is not confirmed.

Boss Battle 4 is also included in Super Smash Bros. Ultimate, where it can be played on any stage from the Metroid series.