Phantasmagoria. Little bit dated, and more severely creepy than mindbuggery, but still good.
There's this part where you find a child's room, a nursery. There's a picture of the infant on the wall, but on the other wall there's a spot in the paint, like the drywall is crumbling or deforming. When you get close to it,
The baby forms out of the wall and tries to grab you.
Also, in the dining area of the mansion, there's a large portrait on the wall. When you pass by it, it's fine.
When you pass by it again, it's not very noticeable, but the portraits eyes are glowing red. When you click on it, your character investigates, only to be nearly strangled by the painting.