This is a full compilation of all the songs used in BFS. Keep in mind that many songs are used multiple times throughout the game.
Lobby/Other
-Welcome to Boss Fighting Stages: Zero Project - Gothic
Chapter 1
-Defeat the enemies, then the boss arrives: SSBM - Fire Emblem
-Initiate: [Boss Spawn]: ROBLOX - Soul Wars
-Well done. Here comes the next wave: Zero Project - Gothic
Chapter 2
-Castle Crashing: ROBLOX - Temple of Master Ninjas
-VS Defender: Ragnarok Online - Monastery In Disguise
-Hit the Levers: ROBLOX - Temple of Master Ninjas
-VS Heavy Knight: Ragnarok Online - Monastery In Disguise
-VS McSlash: Ragnarok Online - Monastery In Disguise
-Crisis Mode!: ROBLOX - Temple of Master Ninjas
Chapter 3
-The Trials: ROBLOX - Temple of Master Ninjas
-The First Trial: SSBM - Fire Emblem
-You can now continue: ROBLOX - Temple of Master Ninjas
-Chartreuse Periastron: SSBM - Fire Emblem
-Yes we don't: ROBLOX - Temple of Master Ninjas
-VS Chartreuse: Ragnarok Online - Monastery In Disguise
-GrimGold Periastron: SSBM - Fire Emblem
-You've gotten far, challenger!: ROBLOX - Temple of Master Ninjas
-VS GrimGold: Ragnarok Online - Monastery In Disguise
-Azure Periastron: SSBM - Fire Emblem
-Your opponent is ME!: ROBLOX - Temple of Master Ninjas
-VS Azuran: Ragnarok Online - Monastery In Disguise
-Spike Castle Parkour: ROBLOX - Temple of Master Ninjas
-VS Azurewrath: Ragnarok Online - Monastery In Disguise
Chapter 4
-King...?: ROBLOX - Temple of Master Ninjas
-Rock Monsters: SSBM - Fire Emblem
-"...": ROBLOX - Temple of Master Ninjas
-VS Stone: Ragnarok Online - Monastery In Disguise
-Great, now I'm soaked: ROBLOX - Temple of Master Ninjas
-Water Monsters: SSBM - Fire Emblem
-He did seem a bit, Stone Cold: ROBLOX - Temple of Master Ninjas
-VS Aqua: Ragnarok Online - Monastery In Disguise
-Washed up...: ROBLOX - Temple of Master Ninjas
-Armored Monsters: SSBM - Fire Emblem
Chapter 5
-The Factory: Woodentoaster - Rainbow Factory
-VS Static: Ragnarok Online - Monastery In Disguise
-Well, that was shocking: Woodentoaster - Rainbow Factory
-VS Techno Devil: Ragnarok Online - Monastery In Disguise
-VS Bass Devil: Caern - Defeater
Chapter 6
-What a bother that you guys are here...: Spore - Space Diplo 5
-You need training: Mother 3 - Hard Rain
-VS Arcane Warlock: Spiral Knights - The Confrontation (Speed x1.07)
-VS Dezadon: SSBB - Fire Field
-VS Spirit Duo: Final Fantasy 10 - Enemy Attack
-VS Crisis Dezadon: SSBB - Fire Field
-VS Crisis Arcane Warlock: Spiral Knights - The Confrontation (Speed x1.07)
-VS Duo Crisis: Kirby Super Star Ultra - Galacta Knight Remix
Chapter 7
-The Final Test: Mother 3 - Hard Rain
-VS Baller: Holoska - Cool Edge
-VS Piercer: Immediate Music - Hostage Crisis
-VS Slicer: CueFonix - Inner Fire
-VS Crusher: Epic Score - Smash Them All
-Explanations: Mother 3 - Hard Rain
-The Asudem: [Unknown]
-The Wraith: The Wraith - Wraith Ambience
-Backstory: Mother 3 - Hard Rain
-Zhao VS Kai: ROBLOX - Temple of Master Ninjas
-With ONE hand?!: Mother 3 - Hard Rain
-King?: Spore - Space Diplo 5
Nostalgia Revived 1: War of Souls
-Captured?: Mother 3 - Hard Rain
-Defend the Castle: SSBM - Fire Emblem
-The Final Gate: Zero Project - Gothic
-VS Soul Weegee: Qumu - Luigi's Mansion Remix
-Pssh, it's nothing personal, kid: Spore - Space Diplo 5
-VS Soul Turdulator: いそえ としみち (Toshimichi Isoe) - Monastery in Disguise (RO 10th Anniversary Edition)
-VS Soul Turdulator [Awakened Mode]: Bravely Second: End Layer - Battle of Providence
-I will return!: Mother 3 - Hard Rain
Nostalgia Revived 2: Noob Defender
-Defend the Statue: Mother 3 - Hard Rain
-Waves 1-19: Waterflame - Jumper
-VS Giant Armour Noob: Waterflame - The Race Around the World
-Waves 21-24: Waterflame - Jumper
-VS Epic Noobs: TheFatRat - Windfall
-VS Siege Noobs: Waterflame - The Race Around the World
-VS Mr. Hammer: The Living Tombstone - Tom's Dog
-VS Mr. Hammer (raig moad): Muzzy - Insignia
-VS Sir Noobalot: The Living Tombstone - Tom's Dog
-VS Sir Noobalot (moar block): Muzzy - Get Crazy
-VS Newbiemancer: xi - Q.E.D. Ripples of 495 Years
-VS Sir Kadee: Waterflame - The Race Around the World
-VS Sir Kadee (Dark Power): Pendulum - Witchcraft (Instrumental Version)
-VS Sir Kadee (Half Bound): Pendulum - Watercolor/Witchcraft Instrumental Mix
-fight u at full stronk next time!1 XD: Mother 3 - Hard Rain
Christmas Wrath
-How MerryWrath Stole Christmas: F-777 - Super Santa
-VS Christmas FOE: F-777 - Snowflakes
-Path to the Pinnacle: F-777 - Super Santa
-VS MerryWrath: F-777 - Icicles
-VS Crisis MerryWrath: F-777 - Toy Factory
Nature Wrath
-Bringing May Flowers: EnV - Green With Me
-VS Spring FOE: EnV - Bloom
-Fortress of Flora: EnV - Green With Me
-VS SpringWrath: EnV - Revive
-VS Crisis SpringWrath: ARForest - Hemisphere
???
-?: Danny Baranowsky - Styx and Stones
-?: Danny Baranowsky - Heart of the Crypt
-?: Danny Baranowsky - Styx and Stones
-?: Danny Baranowsky - The Wight to Remain
-?: Danny Baranowsky - Styx and Stones
-?: Danny Baranowsky - For Whom the Knell Tolls
-?: Danny Baranowsky - Styx and Stones