Me and mouseflash had some ideas for hn2 here are some of them.
Tv noises:these could be used to drop lore hints and make the museum and other locations a bit more eerie.
Soundtrack idea:we had an idea for when you reach the end of your journey a bit of false hopeful music plays. Which would sorta foreshadow if something bad were to happen.
The Guest teleporting:if the guest ended up teleporting at some point in the game(which I'm pretty sure he can) they could give him a little darkness around him.
I think that's all the ideas we had. If there are any more I forgot I will add them