The monster under the bed is designed to be a little cute. Although the theme is Spooky Monster, a slightly cute looking monster seems fitting ina children's bedroom. It is a blob shape covered in fur, with a single eye with a red laser inserted into it. This allows the team of explorers to only need to control the movement of one laserbeam in the room, as opposed to more than that if the monster had more eyes.
The cuteness of the monster will be less obvious since it won't be too visible. The room is dimly lit by night lights, and the monster is under the bed, which shrouds it in darkness, making the laser even more obvious.
The monster also needs to be able to detect when it is hit with a laser beam. This will affect the material used to cover the monster so that it has this capability.