Instructions
Paint the two skulls on the wall of the foyer.
Head up the stairs to the library and talk to Madam Leona, the floating head in the jar. She'll tell you to paint all the skulls in the house to calm the poltergeist. This also opens the exit in the Lonesome Manor.
Go right to the balcony and paint the skull behind the moving bookcases. Head to the opposite side of the room and paint the skull on that side.
Move between the two bookcases in the hallway and use paint thinner on the red spot on the floor. Jump on the switch that's revealed and paint the skull on the wall quickly.
Go into Mad Doctor's lab. Use paint thinner to weaken his cronies and destroy the two generators in the front of the lab. Destroy the back generator with paint thinner as well. Spray more paint thinner on the red eye inside the generator to kill the doctor.
Go back down to the foyer and the front door will be open if you painted all of the skulls in the house.