- This article is about the theme from Return of Samus. For the theme from Metroid Prime, see Metroid Battle Theme.
This theme is played during every encounter with Metroids from Phase 1 through Phase 8. Therefore, it serves as the shared boss theme of Alpha Metroids, Gamma Metroids, Zeta Metroids, and Omega Metroids. The Metroid larvae and Queen Metroid are the only Metroids with their own separate battle themes.
This theme opens with a shrill stinger, often accompanying a short cutscene of one Metroid stage metamorphosing into the next. The rest of the song consists of looping variations of a four note melodic pattern, in which the first two notes descend in pitch and the next two notes ascend in pitch. The harmony is evocative of alarms or sirens. Occasionally, the pattern is punctuated by a series of frantic high-pitched notes. The theme can be heard here: 
Multiple boss themes in Metroid: Samus Returns seem to reference the original Metroid battle theme. Boss Alpha2 features a repeating four-note phrase that is very similar to this theme, and may even be intended as an arrangement. Boss Arachnus has a nearly identical opening stinger, and its harmonic patterns are reminiscent of this theme's melody. Boss Zeta features a similarly shrill opening stinger as well.