Mariugh was an ancestor of Mario from the caveman days. Unlike his counterpart, he is naked. (Though his counterpart has a habit of streaking).
After SMG4 and Toad got send to the past, they encounter a giant Yoshi. As the other cavemen fled in terror, the Yoshi was suddenly attacked by Mariugh and Luigar. Mariugh managed to knock the Yoshi down in one punch. Afterward, SMG4 and Toad approached the Caveman Bros., surprised by their resemblance to Mario and Luigi. At first, the Caveman Bros acted hostile, but SMG4 tried to offer them spaghetti as a peace offering, which they eat after Toad told them how to. Mariugh and Luigar became so enticed with the taste that they quickly befriended the strangers. They then carried SMG4 back to their home, with Toad following behind them.
However, it did not go as expected, as Mariugh made SMG4 uncomfortable when he tried to seduce him with a drawing of an LGBT-related show on the stone TV in the background. SMG4 and Toad tried to come up with a plan on how to escape. The former decided to distract the Caveman Bros. by putting on a video of Barney the Dinosaur for them.
While trying to leave, SMG4 came across a drawing that the brothers made of them, considering the strangers as their friends. Extremely touched, SMG4 realized that they were just trying to help. Mariugh and Luigar suddenly find them and tell them that they were able to find someone that could help: E. Gadd's ancestor, Professor E. Gugh. However, E. Gugh's solution appeared to be to simply knock SMG4 out with a rock.
By replacing the time machine remote's batteries, the portal emerged in the cave, catching the entire group's attention. SMG4 and Toad walked back through the portal and returned to the Present. To their surprise, Mariugh, Luigar, and E. Gugh also followed them through the portal. The arrival shocked Mario, Luigi, and E. Gadd, who each tried to take a moment to get acquainted with their ancestors. Eventually, E. Gadd had to send them back through the portal to prevent a time paradox. After their primitive counterparts said goodbye and left, SMG4 broke down in tears, while Toad ranted once more time about them mistaking him for a melon.