She is a little girl, who appears only in the dark. Little is known about her, although she seems to be the sister of Asmodeus and the Fire Babies. She occasionally appears at random times without warning, doing various things to make the player jump. She can appear after certain things the player does, such as turning around, opening a door, or putting down the map. She might do a "Peek-a-boo" at the player, sneak behind the map, or even run and scream/laugh.
In the above cases, she cannot harm the player. However, in Dungeon Nightmares II, she can actually harm the player, but very rarely. When opening a chest, she might appear sitting on top of it and laugh. She disappears in less than a second. When that happens, the player will receive some damage. So, it is advised to never open a door, or treasure chest before healing completely.
Her face can be seen at the top of the configuration window of the game.