The Black Creature is an enemy that the player encounters when they walk through the hallway past the statue. It poses no threat however as an image of Ellen will protect Viola from the Black Creature.
In Extra Mode it is much more of a threat as it can actually kill Viola by ripping of her face. In order to prevent the creature from attacking, the player must simply walk into the light from the window to the right of Viola, then the image of Ellen will appear.
It is entirely black, except for part of its face, and it appears to have no legs. This may represent Viola in Ellen's body attempting to get her body back, but the House is protecting Ellen from such an act and allows her to go on and escape.