I think it would be cool if the guest would stalk you during the day and whenever it's night and you need to go to the museum, he would actually try to catch you. This is where the flashlight could be implemented, because it's not in the game yet (iirc) for some reason. He would try to jumpscare you like in HG and you would need to use the flashlight to counter him. During the night, he will have his normal guest design and the cloak in the DLC.
I think that would be a good way to implement him aside from the DLC.