So I was reading through this thread and saw that people were sharing what custom music they had. So I decided to share my custom music.
Battlefield
Battlefield -> Battlefield (Melee)
Menu (Super Smash Bros. Melee) -> Break the Targets! (Melee)
Battlefield Ver. 2
Battlefield (Melee) -> Subspace Emissary Boss Battle 1
Multi-Man Melee 1 (Melee)
Final Destination
Final Destination
Credits (Super Smash Bros.)
Opening (Melee) -> Multi-Man Melee 2 (Melee)
Final Destination (Melee)
Giga Bowser (Melee) -> Master Hand Fight (64)
Delfino's Secret - replaces Delfino Plaza
Delfino Plaza
Title / Ending (Super Mario World) -> Super Mario 2007
Main Theme (New Super Mario Bros.) -> Athletic Theme (New Super Mario Bros.) (SSB4)
Ricco Harbour -> Beach Bowl Galaxy
Main Theme (Super Mario 64) -> Throwback Galaxy
Luigi's Mansion
Luigi's Mansion Theme
Castle / Boss Fortress (Super Mario World / SMB3) -> Luigi's Mansion Series Medley
Airship Theme (Super Mario Bros. 3) -> Waltz of the Boos
Tetris Type A
Tetris Type B -> Ghost House (Super Mario World)
Bowser's Castle - replaces Mario Circuit
Mario Circuit -> Bowser's Castle Ver. M
Luigi Raceway -> Koopa Road
Waluigi Pinball -> Castle Theme (Super Mario 3D World)
Rainbow Road -> Baby Bowser Battle (Yoshi's Island)
Mario Tennis / Mario Golf -> Castle / Fortress (Yoshi's Island)
Title (3D Hot Rally) -> Airship Theme (Super Mario Bros. 3)
Excite Truck -> Bowser's Castle (Mario Kart 7)
Metal Cavern - replaces Mushroomy Kingdom
Ground Theme (Super Mario Bros.) -> Metal Battle (64)
Ground Theme 2 (Super Mario Bros.) -> Metal Battle (Melee)
Gritzy Desert -> Metal Cap Theme (Super Mario 64)
Underground Theme (Super Mario Bros.) -> Hazy Maze Cave
Underwater Theme (Super Mario Bros.) -> Underground Theme (Yoshi's Island)
Underground Theme (Super Mario Land)
Peach's Castle - replaces Rainbow Cruise
Rainbow Cruise (Melee)
Princess Peach's Castle (Melee)
Rumble Falls
Jungle Level Ver. 2
Jungle Level -> Gear Getaway
King K. Rool / Ship Deck 2 -> Gangplank Galleon (name fix)
Bramble Blast -> Stickerbrush Symphony (again, name fix)
Battle for Storm Hill
DK Jungle 1 (Barrel Blast) -> Fear Factory
The Map Page / Bonus Level -> Minecart Madness
Kongo Jungle - replaces 75m
Donkey Kong -> Kongo Jungle (64)
Opening (Donkey Kong) -> Jungle Japes (Melee)
25m BGM -> DK Rap
Yoshi's Island (Brawl)
Obstacle Course
Ending (Yoshi's Story) -> Athletic Theme (Super Mario World)
Yoshi's Island
Flower Field
Wildlands - Yoshi's Island Medley (SSB4)
Yoshi's Story - replaces Yoshi's Island (Melee)
Yoshi's Island (Melee) -> Yoshi's Story (Melee)
Super Mario Bros. 3 (Melee) -> Ending (Yoshi's Story)
Hyrule Castle - replaces Bridge of Eldin
Main Theme (The Legend of Zelda)
Ocarina of Time Medley
Title (The Legend of Zelda)
The Dark World -> The Dark World / Dark Dungeon
Hidden Mountain and Forest
Hyrule Field Theme
Main Theme (Twilight Princess) -> Twilight Field (Hyrule Warriors)
The Hidden Village -> Hyrule Field: 1st (Hyrule Warriors)
Midna's Lament -> Gerudo Valley (25th Anniversary Symphony)
Pirate Ship
Dragon Roost Island
The Great Sea
Tal Tal Heights -> Tal Tal Heights (Original) (the brawl remix isn't even tal tal heights)
Song of Storms
Gerudo Valley -> Ballad of the Wind Fish (brawl lost track)
Molgera Battle -> Clock Town (Third Day)
Village of the Blue Maiden -> Great Bay (Melee)
Termina Field -> Saria's Song (Lost Woods)
Temple
Great Temple -> Skyloft (Hyrule Warriors)
Temple (Melee)
Norfair
Main Theme (Metroid)
Ending (Metroid) -> Lower Norfair (only replaced this song because it's one of the only ones that doesn't freeze the game)
Norfair
Theme of Samus Aran, Space Warrior
Battle Scene / Final Boss (Golden Sun)
Marionation Gear
Frigate Orpheon
Vs. Ridley
Vs. Parasite Queen
Opening / Menu (Metroid Prime) -> Escape (Metroid)
Sector 1
Vs. Meta Ridley -> Brinstar Depths (Melee)
Multiplayer (Metroid Prime 2) -> Nemesis Ridley (Other M)
Brinstar (Planet Zebes)
Brinstar (Melee)
Brinstar Depths (Melee) -> Title (Metroid)
Dream Land - replaces Green Greens
Green Greens (Melee) -> Dream Land (64)
Fountain of Dreams (Melee) -> Green Greens Ver. 2 (SSB4)
Fountain of Dreams - replaces Mario Bros.
Mario Bros. -> Fountain of Dreams (Melee)
Gyromite -> Masked Dedede's Theme
Famicom Medley -> C-R-O-W-N-E-D
Power-Up Music -> Grape Garden
Mysterious Murasame Castle -> Forest / Nature Area Ver. 2 (SSB4)
Halberd
Revenge of Meta Knight
The Legendary Air Ride Machine
Gourmet Race
Butter Building
King Dedede's Theme
Squeak Squad Theme -> Galacta Knight's Theme
Vs. Marx -> Dark Meta Knight's Theme
02 Battle - > The World to Win
Boss Theme Medley -> Boss Battle (Return to Dream Land)
Checker Knights
Forest / Nature Area -> Another Dimension
Frozen Hillside
Corneria (Sector Z, Venom)
Corneria (Melee)
Venom (Melee)
Lylat Cruise
Space Armada
Corneria
Main Theme (Star Fox)
Main Theme (Star Fox 64)
Area 6
Area 6 Ver.2 -> Area 6 / Missile Slipstream
Star Wolf
Star Wolf (Star Fox: Assault)
Space Battleground
Break Through The Ice
Tunnel Scene (X) -> The Loner, Falco Lombardi (brawl lost track)
Saffron City - replaces Jungle Japes
Jungle Japes (Melee) -> Kanto Trainer Battle (HG/SS)
Kongo Jungle (Melee) -> Silph Co.
Pokemon Stadium
Pokemon Stadium (Melee) -> Johto Gym Battle
Battle Theme (Melee) -> Champion Blue Battle (World Champion Ver.)
Poke Floats (Melee) -> Unova Elite Four Battle
Pokemon Stadium 2
Pokemon Main Theme -> Champion Lance / Red Battle
Road to Viridian City -> Wally's Theme (Omega Ruby / Alpha Sapphire)
Pokemon Center -> Hugh Battle Theme
Pokemon Gym / Evolution -> Silver Battle Theme
Wild Pokemon Battle (Ruby / Sapphire) -> Colress Battle Theme
Spear Pillar
Victory Road
Dialga / Palkia Battle at Spear Pillar -> Giratina Battle Theme
Wild Pokemon Battle (Diamond / Pearl) -> Champion Cynthia Battle Theme
Team Galactic Battle
Route 209 -> Mt. Coronet
Onett
Mother (Melee) -> Bein' Friends / Eight Melodies (Melee) (another name fix)
Mother 2 (Melee) -> Pollyanna (Melee) (yet another name fix)
Fourside - replaces New Pork City
Porky's Theme -> Fourside (Melee)
Unfounded Revenge / Smashing Song of Praise
Mother 3 Love Theme
You Call This A Utopia?! -> F-F-Fire! (The Alternative)
Humoresque of a Little Dog
Snowman -> Porky Means Business!
Port Town Aero Drive (Port Town X)
Mute City
Fire Field
White Land
Car Select
Dream Chaser
Devil's Call In Your Heart
Climb Up And Get The Last Chance!
Brain Cleaner
Shotgun Kiss
Planet Colors -> Theme of Captain Falcon
Golden Forest -> Rainbow Road (F-Zero X)
Mach Rider (Melee) -> Mute City (Mario Kart 8 )
Big Blue
Big Blue (Melee)
Mute City (Melee) -> Big Blue (Mario Kart 8 )
Infinite Glacier - replaces The Summit
Ice Climber
Balloon Trip
Clu Clu Land
Shin Onigashima
Icicle Mountain (Melee)
Castle Siege (Coliseum Omega)
Fire Emblem Theme -> Id Purpose
With Mila's Divine Protection
Attack -> Id Hope
Preparing to Advance -> Destiny (Ablaze)
Winning Road - Roy's Hope
Shadow Dragon Medley -> Tearing Shadows
Ike's Theme -> Eternal Bond (Ike's Theme) (the PMDT fixed this one themselves)
Against the Dark Knight -> The Devoted
Crimean Army Sortie -> Recruitment Theme Medley
Power-Hungry Fool -> Conquest (Ablaze)
Victory is Near -> More Than Just Comrades - Fire Emblem Remix
Fire Emblem (Melee) -> Together We Ride (Melee) (name fix)
Flat Zone 2
Flat Zone 2
Chill (Dr. Mario)
Flat Zone (Melee)
WarioWare Inc.
WarioWare Inc.
WarioWare Inc. Medley
Ashley's Song
Ashley's Song (JP) -> Ashley's Song (JP) Ver. 2 (SSB4)
Mike's Song
Mike's Song (JP)
Mona Pizza's Song
Mona Pizza's Song (JP)
Skyworld
Underworld -> The Return of Palutena
Skyworld -> Boss Fight 1 (Kid Icarus: Uprising)
Title (Kid Icarus) -> In the Space Pirate Ship
Kid Icarus Original Medley -> Dark Pit's Theme
Distant Planet
Main Theme (Pikmin)
World Map (Pikmin 2)
Stage Clear / Title (Pikmin)
Forest of Hope
Ai no Uta
Ai no Uta (French) -> Eterna Forest
Tane no Uta -> Stage Select (Pikmin 2)
Environmetal Noises -> Viridian Forest (HG/SS)
Title (Big Brain Academy)
Smashville
Main Theme (Animal Crossing)
Go, K.K. Rider!
2:00 a.m. -> Plaza / Title (Animal Crossing: City Folk / Wild World)
The Roost -> Kapp'n's Song
Town Hall / Tom Nook's Store -> Bubblegum K.K.
Hanenbow
Hanenbow Ambience - Hanenbow (PM)
PictoChat
PictoChat
Mii Channel
Wii Shop Channel
Brain Age (Train Your Brain In Minutes A Day)
Opening (Wii Sports)
Charge (Wii Play)
Shaberu DS Cooking Navi
Lip's Theme (Panel de Pon)
Fever (Dr. Mario) (Melee) (name fix)
Mario Galaxy - replaces Green Hill Zone, GHZ is now a stage expansion stage (I want more songs for mario galaxy)
Green Hill Zone -> Good Egg Galaxy
Angel Island Zone -> Gusty Garden Galaxy
Scrap Brain Zone -> Rosalina in the Observatory / Luma's Theme
Emerald Hill Zone -> Purple Comet
Sonic Boom -> Sky Station Galaxy
Super Sonic Racing -> Bowser Jr.'s Theme
Open Your Heart -> Battlerock Galaxy
Live and Learn -> Space Junk Galaxy
Sonic Heroes -> Bowser's Galaxy Generator
Right There, Ride On -> Super Mario Galaxy
HIS WORLD (Instrumental) -> Champion's Road
Seven Rings In Hand -> Rainbow Road Medley
Also the PMDT announced an Awakening Roy alt.