From the Super Mario Wiki
The Mushroom Referee appears as a minor character in The Adventures of Super Mario Bros. 3 episode "Tag Team Trouble". When he is not hosting wrestling matches, he is apparently in charge of signing people up for them, as can be shown in the episode itself.
The Mushroom Referee hosted the Tag Team Wrestling Tournament which started before he was ready due to Cheatsy ringing the bell early. Despite his job, the referee didn't seem to care about any of the tricks that the Sledge Brothers were pulling on Mario and Luigi during the match, as he almost declared the Sledge Brothers the winners.
With their opponents down, the referee declared Mario and Luigi the winners of the match. Before the referee could award them with their prize money, Toad took it right out of the referee's hands, as he was in a hurry to use the money in order to resolve a mixup that never even happened.