Muigi is a counterpart of Luigi and the brother of Lario. He and Lario first appeared in Mario Goes to Skate City. Muigi's brother Lario is the one who introduced Lego Racing to MarioMario54321's videos. He is a very famous Lego Racer, and his dream is to become the best Lego Racer of all time, even better than Lego Racer's own Rocket Racer. He has a Weegee counterpart named "Meegee", who instead of scaring people with it's stare, is very annoying when he goes "Go Meegee!" over and over again. Muigi usually communicates with Lario and other characters through his counterpart Meegee when outside of Super Mario 64.
Lario and Muigi made reappearances in Adventure 101, a 9-part series that got started after a user named releb101 paid MarioMario54321 in ROBUX to do a 9-part series featuring him. This is when he worked his way up to challenge Rocket Racer to a race. Having beaten him, he won a giant number 1, which together with a giant number 0 and another giant 1, made 101.
Muigi and Lario were tritagonists in The Adventures of Johnny and Marine, another 9-part series made by MarioMario54321 that continued Muigi's Lego Racing adventures. This is when he filled Johnny Thunder's car with sand after losing to him, causing him to crash into an island where he meets Marine the Racoon. He later raced Johnny Thunder again after confessing and apologizing to him for what he did, and won.
Muigi returned with Lario once again in Muigi's Road to LEGO Racing Fame! to race in the courses that he had not raced in in order to have raced and won in every course. After that, he challenged Rocket Racer to one more race, to see who was the best. Muigi beat Rocket Racer and became the best Lego Racer of all time!
Muigi and Lario made an appearance in MarioMario54321's Christmas Carol, where some events from The Adventures of Johnny and Marine were continued.
Muigi and Lario reappeared once again in Twenty-leven where his counterpart Meegee lost faith in himself because there was another Meegee who was more known and looked like Mario. He decided to go back to the Lego Racing world and stay there, where he was loved and famous for being the best Lego Racer of all time, leaving Muigi in Super Mario 64 as a nobody, and perfering it be that way so that he, Lario and everyone else could be there in peace. Muigi later reappeared with Lario in OiramOiram12345 and the Dark Star X to face his evil doppleganger, Igium.
- Muigi and his counterpart Meegee sometimes have a split personality, which was somewhat revealed in Twenty-leven.
- Muigi does not overuse words such as "anyway" like Lario does.
- Videos that star or feature Muigi and/or Meegee are not very popular due to the fact that their videos have little views.
- Muigi first revealed that he was a Lego Racer in Adventure 101, even though it was Lario who first did it in Mario Goes to Skate City.
- He looks similar to Fourigi