Boss Gamma

Vs. Gamma Metroid (as named internally), also known as Boss Battle 2, is a chaotic battle theme from Metroid: Samus Returns. It is composed by Daisuke Matsuoka.

Description
Vs. Gamma Metroid plays during encounters with Gamma Metroids. It is a frantic and energetic fast-paced battle theme, with electronic instrumentation and an emphasized beat. It can be heard here:

Vs. Gamma Metroid appears to be an original composition, not based upon any of the songs composed by Ryoji Yoshitomi for Metroid II: Return of Samus. While this track is not confirmed to be a remix of any preexisting Metroid songs, some of its melody is reminiscent of the Parasite Queen battle theme, and its driving beats are evocative of the B.O.X. Security Robot battle theme.

Trivia

 * When Gamma Metroids are encountered in superheated rooms, this theme does not play. Instead, a remix of the Lower Norfair theme continues to play during those battles.