Mario, Luigi, and Toad find out that there's been a Rabbit who's eaten so much chocolate that it has literal explosive diarrhea due to eating chocolate for a full year.
SMG4 and the rest of the cast from the previous addition have been kidnapped by Admiral A.S.Swipe, and now their only hope for a rescue lies with a mysterious figure.
When Luigi accidentally runs over Mario's spaghetti while driving drunk, Mario demands money from Luigi for a new one. The problem? Luigi has no money.
SMG3 takes the villain spotlight from Bowser when he unveils his ultimate masterstroke to dispose of SMG4: uploading a 100-hour long video to YouTube of SMG4 at his worst moments he calls, "SMG4 exposed".
Mario is kidnapped, put on trial, and shortly thereafter sentenced to execution by the Goombas, who have gone rogue from Bowser's army due to Mario jumping on and subsequently killing so many of them over the years.