|This article is written from the Real Life point of view|
Vs. Ridley consists largely of a repeating four note phrase, where the first two notes are longer and held on a single pitch, and the second two notes are shorter and rise and fall in pitch. This repeating phrase is broken up by two melodic sections that are generally quieter and more suspenseful, serving to build up tension as they rise up the scale; typically, the first interval is heard halfway through the loop, and the second is heard at the end of the loop.
Vs. Ridley is present in all Metroid games featuring Ridley, with the sole exception of the original Metroid. Every variation features new notes and sounds, but are always consistent with the original.
In its debut in Super Metroid, the original theme is used not only for both battles against Ridley, but also for Draygon and both forms of Torizo. Therefore, it was originally titled Big Boss Confrontation BGM (Ridley, Draygon) (大ボス対決BGM （リドリー，ドレイゴン）), following a similar naming scheme as Big Boss Confrontation BGM (Kraid, Crocomire, Phantoon). It can be heard here: .
The theme is used as the escape theme for both Ceres Space Colony and Zebes, albeit with the percussion removed and an additional alarm wail added. Although this version's instrumentation and composition is otherwise unchanged, it is given a separate track on soundtrack albums, titled Escape (脱出). It can be heard here: .
The original battle and countdown versions of the theme are included on Super Metroid: Sound in Action, and later the 1996 SNES compilation album Play it Loud! Original Soundtrack Volume 1 offered by Nintendo Power.
Metroid Fusion features a slower paced arrangement for Neo-Ridley, appropriately titled VS. Neo-Ridley (VS.ネオリドリー). In addition to the slower tempo, its style is simpler and quieter than the original version from Super Metroid. It can be heard here: 
Like in Super Metroid, an alternate version of Vs. Ridley is used for the escape theme. This track, titled Station Escape Timer Mission (ステーション脱出タイマーミッション), is even faster paced than the original, but features even simpler instrumentation than VS. Neo-Ridley. It can be heard here: 
One of the unused tracks present in the game is yet another variant on the theme, but in a regular meter.
In Metroid Prime, the theme was remixed into Vs. Meta Ridley. In addition to a more electronic instrumentation, Vs. Meta Ridley notably adds a new melodic section not present in the original Vs. Ridley. also featured in Metroid Prime 3: Corruption and Super Smash Bros. Brawl.
Metroid Prime Hunters: First Hunt contains an arrangement of the Meta Ridley theme as well, despite his absence in the game. In Nintendo Land, the Metroid Blast Assault Mission has an orchestrated remix of Vs. Meta Ridley theme. In Metroid: Samus Returns, three remixes of Vs. Meta Ridley are used during the Proteus Ridley battle, including one with a similar tempo to VS Neo-Ridley.
In Metroid: Zero Mission one remix is used while fighting Ridley, replacing the Tourian theme that played in the original game. This remix is designated as 15 in the Sound Test. It has the first half repeat twice before continuing with the second half, unlike most versions of the theme. It can be heard here: .
Another remix is used while fighting Mecha Ridley. This version designated as 22 in the Sound Test. It begins with the final notes of the second melodic interval, and features a "grittier" aggressive instrumentation along with electronic sounds to evoke the boss's robotic nature. It can be heard here: 
Metroid Prime Pinball contains a remix of Vs. Ridley theme for the battle against Meta Ridley. While it has similar instrumentation to Vs. Meta Ridley, this version lacks the new melodic section and therefore adheres closer to the original Vs. Ridley. It can be heard here: .
Super Smash Bros. Brawl introduces a metal remix of Vs. Ridley to the Super Smash Bros. series, arranged by Yusuke Takahama from Sega. It opens with the first melodic interval, and plays around with repeating portions of the second interval. This theme is played on Frigate Orpheon as well as an Event Match on Norfair. It also is played for both Ridley boss fights (regular and Meta Ridley) in Adventure Mode: The Subspace Emissary. It can be heard here: .
This remix of Vs. Ridley returns in Super Smash Bros. for Wii U and Super Smash Bros. Ultimate. In Wii U, it is moved to Pyrosphere, where it is the most played track by default, due to the removal of Frigate Orpheon. In Ultimate, it has been renamed Vs. Ridley (Brawl) and can now be played on any stage from the Metroid series. It is also featured as the soundtrack for A Piercing Screech, the trailer revealing Ridley as a playable character in Ultimate.
In Metroid: Other M, the theme was orchestrated as Nemesis Ridley, also known as Theme of Ridley. This remix is also featured in Super Smash Bros. for Wii U, Samus Archives Sound Selection, on the Geothermal Power Plant stage in Dead or Alive: Dimensions, and in Super Smash Bros. Ultimate.
Jam With the BandEdit
In the instrument trivia, Vs. Ridley is played to demonstrate the synth bass.
In Super Smash Bros. Ultimate, a new metal remix of Vs. Ridley is introduced, in addition to the three returning versions from previous games. Remixed once again by Yusuke Takahama, it made its debut during 65: Ridley. This version is arranged similarly to the Brawl remix for the first refrain of the song, but then introduces quieter suspenseful sections that use more orchestral instruments (including a music box at one point) to contrast the intense and aggressive metal sections, ultimately building up to a big and dramatic finish. Aspects of Theme of Samus and Nemesis Ridley can be heard at different points of the song. It can be heard here: