He is a murderer clown just like Jojo. He also works for Zomboss. He was given a task to kidnap Casey, Jeffery, and Randy. He succeeded very well actually with Chill Mushrooms. He was later then killed and turned into a zombie by Diggy. Just like Arthur.exe, he can also teleport to people, and not just locations.
He has a special attack called "ran ran ru" which after he says that, he can imagine the person he's fighting to explode. It then happens in reality. He doesn't even need to use his arms when fighting. Heck when he used Chill Mushrooms, they just float. He tried to get AGK and end him. However, he failed both times. The second time nearly killed him as he got punched off a high stairway. Lego Mario had noticed it. When Lego Mario looked back after a fight he had in the zombie lair, he was gone. He developed a hate for AGK, and would only spare him if he ate a Big Mac. AGK still said otherwise.
He's actually been in Zombie Force for a couple years. He was running his own business, and his introduction was him being a liar. He said his fast food makes you unfat, and you become healthy. However, Bomb called him out for being fat too, so he lied again and said a law exists. This law claims if you own a fast food place, you can't eat your own fast food. When Fire Mario called him weird, this is when he became a problem. Fire Mario & Lego Mario later lied when he heard, saying his food was good. But then oddly enough, he asks for a hug. It was pretty normal actually. Then Fire Mario asked if he hugged little kids, and Ronald McDonald replied with yes. They got scared and tried to get in the car, but then he blocked it asking for another hug. After a distraction they tried to drive away, but the car eventually ran out of gas. Quickly as hell, he ran towards them even if they were far away. He threatened them to keep eating even if they were not hungry. He got them tied to a string, and he was pulling them as they tried to keep running. This sucked for Lego Mario cause both sides were pulling on him.
Eventually, Ronald McDonald won this part of the battle. They were brought back to the fast food place, and turns out he was lying about feeding them. Him and Squidward made a deal with a zombie, and they would survive if the zombie got to eat Lego Mario and Fire Mario. Ronald McDonald & Squidward eventually ran away, and Lego Mario & Fire Mario fought back against the zombie. They won after Lego Mario exploded him. A theory suggests he was already a zombie much earlier, and well this can easily be debunked. It started when he kept saying "hungry hungry" around the Dump House. This made Fire Mario & Blue Toad head back to McDonalds to kill him. Diggy told him, if he doesn't get a brain that day, he'll eat him. After a huge fight occured, Ronald McDonald took out his revenge on Diggy. This resulted to Diggy trying to eat him, but Fire Mario drove everyone over which stops this. But then again, Fire Mario claims him a zombie. He gets up and flips the car.