Have you ever played Luigi's Mansion? Wellllll he's pretty much the exact same character as he is in that game... except he talks more! ...but not much more.

This is a pretty minor role despite him being the main character, so I'd recommend auditioning for multiple roles along side his.

As for his voice, I'm not looking for something super professional or anything, just try to sound like how Luigi does in his games. Also, try to sound frightened as much as possible for lines 2 & 3 since a lot of his lines are like those ones.