Stage music
In the Super Smash Bros. series, each stage has one or more music tracks assigned to it. In Super Smash Bros., Super Smash Bros. Melee, and Super Smash Bros. for Nintendo 3DS, each stage has default music that will always play under ordinary circumstances. Certain stages in Melee and all stages in 3DS have alternate music that can be forced to play, or otherwise has a rare chance to play.
Super Smash Bros. Brawl introduced the My Music feature, which gives each stage a pool of music to choose from; the chance that each song has to play can be adjusted manually. This feature returns in Super Smash Bros. for Wii U and Super Smash Bros. Ultimate.
In Super Smash Bros.
Super Smash Bros. is the only game without alternate music, so all stages only play their single assigned song.
In Super Smash Bros. Melee
Melee was the first Smash Bros. game to introduce more than one song for each stage, in the form of alternate music. Every time a stage is loaded, there is a 12.5% the alternate music will play; however, if all human players hold L or R when the stage loads, the alternate music will always play.
Unlike future iterations, only a set amount of stages have alternate music. Additionally, the songs must be unlocked. Temple and Great Bay gain their alternate music when Marth and Young Link are respectively unlocked; all others are only available upon unlocking every character.
In Super Smash Bros. Brawl
With My Music, each stage (except Hanenbow) has a pool of two to twelve songs to choose from. Bolded tracks must be unlocked.
In Super Smash Bros. for Nintendo 3DS
In 3DS, each stage has a default track and an alternate track. Alternate music has a 15% chance of playing under ordinary circumstances, or can be forced to play by holding the R button while selecting a stage.
In Super Smash Bros. for Wii U
My Music returns from Brawl, and each stage has a greater variety of music to choose from. Unlike Brawl, certain stages also share songs between them. Bolded tracks must be unlocked.
In Super Smash Bros. Ultimate
The My Music feature returns in Super Smash Bros. Ultimate. It has been adjusted so that stages from the same series share the same pool of music; additionally, the default settings for each stage have one song set to the highest and another song set slightly lower, in effect giving them default and alternate music.