The Invisible Monkey is a Secret Monkey found in the Castle Frightmare! level of Ape Escape 2. To find it you have to first go to the side room off to the right after the chair platforms. After you enter the room there will be a fire place to the left. Use the Water Cannon to put out the fire and walk through the fire place. On the other side there should be a stone bust, break it open with the Magic Punch to find The Invisible Monkey.
Stomach fullness: 3/5
Pants type: white
Green potion? What green potion!?