The third character from the free game Ib. Originally unplayable, the update for version 1.4 of the game included a small part where the story is told from her perspective.
Mary is a blond girl with blue eyes, wearing a green dress. Often depicted with a paint knife.
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Actually the final antagonist, Mary is a painting that came to life. She'll try to kill Garry and Ib in order to take their place.