From the Super Mario Wiki
The Mushroom Referee is a Mushroom man who works for the Mushroom Wrestling Federation. He is in charge of signing people up for wrestling matches, which he then referees. He appears as a minor character in The Adventures of Super Mario Bros. 3 episode "Tag Team Trouble" as the host of the Tag Team Wrestling Tournament. Despite being the referee, he does not seem to care about dirty tactics being employed by the Sledge Brothers during the match, nor the use of a Starmen by Mario and Luigi to win the tournament.