YouTube user BIGREEN unleashed the fan-made video yesterday, outlining in the description that there were no mods used in-game, instead, the Among Us character was drawn on top of the game!
Yesterday during the Nintendo Direct, players of Super Smash Bros. Ultimate were treated to another new fighter that isn’t a swordsperson (instead it is the sword itself, but still!).
The Japanese channel posted in October 2020 an earlier mock-up announcement of Classic Mario joining the fight in another very detailed video.