Mary O.

'''Mary O. 'is the manual's guide in Super Mario Maker''. She is available to be spoken to at any time from the game's menu, by tapping the green manual icon. The game's manual can also be accessed online on the official website. Her role is to assist the player, and share information about the game's content. Her appearance is that of a young female with blue eyes and dark hair, and a headset on. Mary O.'s name is deliberately a pun on a common mispronunciation of Mario's name.

A March 2016 update allows players to play as Mary O. in a construction outfit, through the Costume Mario power-up. To unlock the costume, players have to clear the special Event Course created after her, titled "Mary O.'s Lunch Break". There are also special Event Courses created by her ranging back to October 2015, though those do not involve her costume.

A series of online comics starring her and Yamamura have been released on the official Super Mario Maker website.