Nintendo

Blue Mario", also sometimes referred to as "Referee Mario", is a recolored Mario character, first appearing in Mario Tennis for the Nintendo 64. He is not playable, but he can be seen sitting in the referee's chair during some matches when one is playing as Mario. "Blue Mario" can also be seen in the multiplayer game of the Super Mario Advance series, but relation to the "Blue Mario" of Mario Tennis 64 is not explicit and thus currently unknown unless confirmed by Nintendo. It is also currently unknown if he is related to Mario or not.