Instructions
Play through the game until Scrooge is terrified and in his room. He will have locked himself in and gone to bed with a chair propped up against the locked door. Use the stylus to tap the mouse under Scrooge's bed to get him to lift his feet. The mouse will go into a mouse hole in the wall.
Tap on the spider above Scrooge's bed. This will cause Scrooge to hide his head under the pillow. Move the stylus back and forth over Scrooge's exposed feet, tickling him. After a few passes he will get out of bed.
Tap the mouse in his mouse hole, which is behind Scrooge at this point. The mouse will start to come out from its hole, which will startle Scrooge. Use the stylus to knock the chair away from the door while Scrooge is startled from the mouse.
Drag the key from the table into the keyhole on the door using the stylus. You'll have to do this quickly while Scrooge is still distracted. Lift the stylus off of the screen once the key is on the keyhole to open the door.