Mario (also known as Mario Mario or Super Mario) is a video game character who has appeared in 3 unique Japanese OVA animations produced in 1989 that adapt him into fairy tales. Their titles were Momotaro, Issun-bōshi (the one-inch boy) and Shirayuki-hime (Princess Snow White).
Mario is also a playable character in the Super Smash Brothers universe, a Nintendo crossover battle game which also includes various Pokemon characters, another Japanese creation which has had an anime and has had bathing scenes.
Super Mario RPG: Legend of the Seven Stars
This came came out in 1996. If a gamer stays at the Marrymore Inn but can't pay the fee, they are forced to work off their tab employed as a Bellhop. During this time they can walk through the room itself, and if they walk to the upper right door, they can step in, and Mario is heard whistling in the shower. He comes out red-faced, indicating it was a hot one.
There is also a bathrobe in the room, but if a player tries to put it on, they are told it is too small for Mario, because he is a portly plumber.
Mario & Luigi: Superstar Saga
This came came out in 2003. When playing Toad, players can hear Mario humming along to the game's music. Toad comments that he hears this, and walks in to investigate. There is a scream, and Toad runs out. He pauses, blushing, then continues to run, and bashes his head into a nearby dresser. A figure wrapped in a towel can be seen walking in the bathroom, their face obscured by steam. It turns out to be Mario, and he is confused at why Toad is lying unconscious on the ground. After momentarily hovering over him, he backs up, and then leaps in the air, landing on Toad and bouncing off, then landing on him again, smashing Toad 3 times in total before backing off.
In Nintendo Power's guide to Super Mario Bros. 2, Mario is depicted taking a bath holding a Scrub Brush