Here is the list of alternate costumes in Super Smash Bros. 6. Like Smash 4, the costume doesn't effect the character, other than the voice if it's a different character. 

Alternate Costumes

Image Costume Character it's on
Mario-Alt6 SSBU.png Builder Mario Mario
Mario-Alt7 SSBU.png Wedding Mario Mario
SMM2luigi.png Builder Luigi Luigi
Princess Peach Wedding Dress.png Wedding Peach Peach
Dry Bowser Artwork.png Dry Bowser Bowser
Wedding Bowser.jpeg Wedding Bowser Bowser

Bowser Jr.-Alt7 SSBU.png

Bowser Jr.-Alt5 SSBU.png

Bowser Jr.-Alt2 SSBU.png

Bowser Jr.-Alt4 SSBU.png

Bowser Jr.-Alt6 SSBU.png

Bowser Jr.-Alt1 SSBU.png

Bowser Jr.-Alt3 SSBU.png

Koopalings Bowser Jr.
ToadetteArt.png Toadette Captain Toad
Link-Alt1 SSBU.png Link (Hero of the Wild) Link
HW Zelda (BoTW).png Zelda (Champion) Zelda
Loz spirit tracks conductor link by o0demonboy0o-d6ygy35.png Engineer Link Toon Link
Ridley-Alt1 SSBU.png Meta Ridley Ridley
Yoshi-Alt7 SSBU.png Yoshi (Yoshi's Crafted World) Yoshi
SailorDee.png Sailor Dee Bandana Waddle Dee
Krystal 10.png Krystal (Dinosaur Planet) Krystal

Pikachu-Libre.png

025Pikachu-Rock Star.png

Pikachu-Pop Star.png

Pikachu-Belle.png

Pikachu-PhD.png

Cosplay Pikachu Pikachu
Ike-Alt1 SSBU.png Ike (Radiant Dawn) Ike
Warriors Lucina Bride.png Lucina (Bride) Lucina
Robin-Alt1 SSBU.png Robin (Female) Robin
Corrin-Alt1 SSBU.png Corrin (Female) Corrin
Byleth-Alt1 SSBU.png Byleth (Female) Byleth
Lyn Blade Lord Spirit.png Lyn (Blade Lord) Lyn
Ephraim (Legendary Lord).png Ephraim (Legendary) Ephraim
EphraimAwakening.png Ephraim (Awakening) Ephraim
Eirika Graceful Resolve Heroes.png Eirika (Legendary) Eirika
FE Eirika DLC.png Eirika (Bride) Eirika
Olimar-Alt4 SSBU.png Alph Olimar
SSBU Wario Overalls.png Wario (Overalls) Wario
Mona warioware coloured line art by balitix-da666cv.png Classic Mona Mona
45 Villager.png Villager (Girl) Villager
Isabelle NH.png Isabelle (New Horizons) Isabelle
Wii Fit Trainer-Alt1 SSBU.png Wii Fit Trainer (Male) Wii Fit Trainer
SSBU Wireframe Mac.png Wireframe Little Mac Little Mac
Shulk (Modern) (NEW).png Shulk (Future Connected) Shulk
Mythra.png Mythra Pyra
Inkling-Alt1 SSBU.png Inkling (Boy) Inkling
Male Octoling with .52 Gal.jpg Octoling (Boy) Octoling
Springtron.png Springtron Spring Man
KiwiPilotwings.png Kiwi Lark
GSFelix.jpg Felix Isaac
Ever Oasis Tethi concept.png Tethi Tethu
Musashi female.png Musashi (Female) Musashi
Art-02.jpg Magical Vacationer (Girl) Magical Vacationer
E37d8e746621696edd248f7b3c97a2bf.png Freya Frey
NanoAcadmeyStudentFemale.jpg Nano Academy Student (Female) Nano Academy Student
LalaEggerland.png Lala Lolo
Dillon - Dead Heat Breakers.png Dillon (Dillon's Dead-Heat Breakers) Dillon
Astral Chain Protagonist Akira Howard Female Official Render.png Akira Howard (Female) Akira Howard
Old Snake.jpeg Old Snake Solid Snake
MGS4 Raiden (MGR).jpeg Raiden (Metal Gear Rising: Revengence - Original Armor) Raiden
Trevor Spirit CoD.png Trevor Belmont Simon Belmont
Simon.jpg Simon Belmont (Castlevania Judgement) Simon Belmont
Young Richter Belmont.jpg Dracula X Chronicles Richter Richter Belmont
Castlevania 1-090708-.jpg Alucard (Castlevania Judgement) Alucard
Official judgment shanoa.png Shanoa (Castlevania Judgement) Shanoa

Black Bomberman R.png

Red Bomberman R.png

Blue Bomberman R.png

Green Bomberman R.png

Yellow Bomberman R.png

Pink Bomberman R.png

AquaBomberman R.png

Bomberman Bros. Bomberman
Pretty Bomberman R-0.png Pretty Bomber Bomberman
WinBee.png WinBee TwinBee
GwinBee - 02.jpg GwinBee TwinBee
Mimipeace.png Mimi Nyami
Classic Sonic - Sonic Forces Artwork.png Classic Sonic Sonic
Bayonetta-Alt1 SSBU.png Bayonetta (Bayonetta 1) Bayonetta
Jeanne gun.png Jeanne (Bayonetta 1) Jeanne
ShujinUniformSSBU.png Shujin High School Uniform Joker
P5ProtagDance.png Dancing in Starlight Attire Joker
DoppelgangerArle.png Doppelganger Arle Arle Nadja
Dark Arle.png Dark Arle Puyo Puyo
RedAmitie.png Red Amitie Amitie
GunstarBlue.jpg Gunstar Blue Gunstar Red
RollyRollBH.png Rolly Roll Billy Hatcher
MeeMee Profile.png MeeMee AiAi
Sakura Amamiya.png Sakura Amamiya Sakura Shinguji
Protoman SSB4.png Proto Man Mega Man
Bass smashified by jdmh dbbyoko-fullview.png Bass Mega Man
Evolryu-ssf4ae-art.jpg Evil Ryu Ryu
Eb561dec2b1b5932e8aeaaa964ecb985-d4lcifv.jpg Chun-Li (Street Fighter Alpha) Chun-Li
Skullomania SNK Heroines.png Female Skullomania Skullomania
SNKCapCardFighters2Morrigan.png Morrigan Aensland's Casual Outfit Morrigan Aensland
LeonRE2Remake.png Leon Kennedy (R.P.D Uniform) Leon Kennedy
ShiranuiOkami.png Shiranui Amaterasu
Pac-man-party-wii-007.jpg Pac-Man (Pac-Man Party) Pac-Man
Heihachi Mishima (PSASBR).png Heihachi (Young) Heihachi
Nightmare 1.png Nightmare Siegfried
Taizo.jpg Taizo Hori (Mr. Driller) Taizo Hori
Klonoa Moonlight Museum Artwork.gif Classic Klonoa Klonoa
Katsu.png Katsu-Chan Don-Chan
Cloud-Alt1 SSBU.png Cloud (Advent Children) Cloud Strife
ErdrickSSBU.png Arusu Hero
SoloSSBU.png Solo Hero
EightSSBU.png Eight Hero
DQB - Heroine.png Builder (Female) Builder
KululunBB4F.png Kululun/Peb Bub
Terry Bogard (Mark Of The Wolves).jpg Mark Of The Wolves Terry Terry Bogard
Mrkarate2 kofmi.jpg Mr. Karate II Ryo Ryo
Kyo kusanagi nests syle by betolavigne-d4h80ff.png Kyo Kusanagi (NESTS Style) Kyo Kusanagi
3dfc940024cd0231d495342a46d336db.png Iori Yagami (KOF XII) Iori Yagami
Athena Asamiya Onginal.png Classic Athena Asamiya Athena Asamiya
SNK Heroines Tag Team Frenzy Nakoruru.png Arabian Nights Nakoruru Nakoruru
SNK Heroines Kula Diamond Diamond Swan.png Diamond Swan Kula Kula Diamond
TarmaMetalSlug.png Tarma Roving Marco Rossi
AlexMinecraft.png Alex Steve
Mugman results.png Mugman Cuphead
Mac-0.png Mac Joe
Order Sol.png Order Sol Sol Badguy
Sol Guilty Gear Strive.png Strive Sol Sol Badguy
Jimmylee-blondehair-bust.png Jimmy Lee Billy Lee
Riki.png Riki Kunio
RCG Misako.png Misako Kyoko
Adol (80's).png Classic Adol Adol Christin
Laharl chan.png Female Laharl Laharl
Ccf8891d64b4698d0d9bdd7c0a0c6d11.jpg KH II Sora Sora
220px-Sora.png KH III Sora Sora
DoomMarineClassicEternal.png Doom Marine (Classic) Doom Slayer
RyuHayabusaClassic.png Ryu Hayabusa (Classic) Ryu Hayabusa
CurlyBrace.png Curly Brace Quote
CocoN.SaneTrilogy.png Coco Bandicoot Crash Bandicoot
NicoleMcCallister.png Nicole McCallister Pitfall Harry
Lily.png Lily Maxwell
Wild-guns-reloaded-20166158519 1.jpg Annie Clint
SoMIGuybrush.png Guybrush (Secret of Monkey Island) Guybrush Threepwood
CoMIGuybrush.png Guybrush (Curse of Monkey Island) Guybrush Threepwood
EFMIGuybrush.png Guybrush (Escape from Monkey Island) Guybrush Threepwood
MW3nT.png Commandgirl Video Commander Video
Community content is available under CC-BY-SA unless otherwise noted.