Junior (The Adventures of Super Mario Bros. 3)
From the Super Mario Wiki
Junior is an out-of-control brat; his parents might actually fear him, as they talk kindly towards him, but can't stand being around him for long. Junior's family also has a pet cat named Kitty, but she appears to have been abused, most likely by Junior. From what his parents implied, they've had great difficulty finding a babysitter for him due to his bad reputation.
At the start of the episode, Junior breaks two vases that he tried to balance upon his head, and places Kitty on the broken pieces, giving his mother the impression that Kitty broke the vase. Afterwards, Mario and Luigi show up unexpectedly, and are coerced by Junior's mother to babysit Junior while they go out for the night (and to get a break from their son). Stuck at home with the Mario bros., Junior demands that they play hide-and-seek, and that Mario and Luigi are "it".
While looking for a hiding spot under the kitchen sink, Junior finds the Warp Pipe that the Mario Bros. came through and warps to the Mushroom Kingdom. Thinking it's the coolest place ever, Junior runs off, attacks a trio of Boomerang Brothers with one of their own boomerangs and runs into Cheatsy, Bully and Kooky. Wanting to annoy Mario and Luigi, Junior agrees to work with the Koopalings. He pretends to be in danger so that Mario and Luigi try to rescue them, but instead, they are lured into a trap.
Although Junior thought that the Koopalings were just playing around, they get suspicious of Junior and toss him down a Warp Pipe to the Pipe Maze, where he gets lost and frightened. Eventually, Mario and Luigi come to his rescue, and help him escape from the Pipe Maze. Junior then helps the Mario Bros. plug a volcano that the Koopalings overloaded with lava, and Mario and Luigi then take him home to Brooklyn.
At home, Mario and Luigi rush to get Junior in the bathtub, because his mother would be angry at them if he didn't bathe. When his mother sees that Mario and Luigi actually managed to give Junior a bath, she asks them if they can babysit the following Friday, to which Junior comments "Oh boy! That would be super!". Mario and Luigi, however, appear less enthusiastic about having another babysitting job.