From the Super Mario Wiki
Mark is a character appearing in three sports games: NES Open Tournament Golf, the Game Boy Color version of Mario Tennis, and Mario Tennis: Power Tour. In NES Open Tournament Golf, he is a young kid who oddly wears blue baseball clothes (as well as a blue hat). The back of his shirt has a large "1". In Mario Tennis, he is on the varsity team. In doubles, the player has to face him and Bob to get in the Island Open. In Mario Tennis: Power Tour, he is the coach of the Junior class at the Royal Tennis Academy.
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