I know you wont luv me the same way

Certain characters whose movesets are directly based on other characters in the game are now classified as "Echo Fighters", possessing similar movesets and proportions to the fighters they are based on, but with their own unique animations and gameplay differences. On the character selection screen, these characters can either be listed individually or stacked with the fighters they are based on. Select characters also have alternative skins featuring different genders or sometimes other characters, such as Bowser Jr. who has a selectable appearance to be any of the other Koopalings but otherwise have identical animations and abilities.Several returning characters received updates to their outfits, such as Mario having Cappy from Super Mario Odyssey accompanying him and Link wearing his outfit from The Legend of Zelda: Breath of the Wild.

Additional fighters have been added to the game via post-release downloadable content (DLC). The first of these, Piranha Plant from the Mario series, was released in January 2019 and made available for free to those who purchased and registered the game with a My Nintendo account before the end of that month.Additional fighters, each coming with a unique stage and related music, have been released both individually and as part of two Fighters Pass bundles. The first Fighters Pass consisted of five characters: Joker from Atlus' Persona, released in April 2019;the Hero from Square Enix's Dragon Quest series, released in July 2019; Banjo and Kazooie from Rare's Banjo Kazooie series, released in September 2019; Terry Bogard from SNK's Fatal Fury series, released in November 2019; and Byleth from Fire Emblem: Three Houses, released in January 2020. 

While Nintendo had originally planned to limit new fighters to those in the initial Fighters Pass, the company announced plans in September 2019 to release additional DLC fighters via Fighters Pass Volume 2, which includes six additional fighters that are scheduled to be released by 2021. Sakurai stated in February 2020 that there are no further plans for any additional Fighters Passes after the second one for Ultimate.The first character in this collection, Min Min from Arms, was released in June 2020. Steve, the player avatar from Mojang Studios' Minecraft, was released in October 2020; with the game's Alex, Zombie, and Enderman characters appearing as alternate costumes. Sephiroth, the antagonist from Square Enix's Final Fantasy Vll, was released in December 2020, with players able to unlock the character a few days before release by defeating him in a limited time boss battle known as the “Sephiroth Challenge”.