So I've heard a few people talk about when a PC dies, bring them back as a ghost is an option. Well I have a PC who wanted to start as a ghost. I originally suggested he died in Death House where the players find him, but when he introduced himself he implied he died somewhere else and came here. So I'm not sure how that works, I assume ghosts can enter Barovia? Would that be an issue?

Also he picked a custom ghost race that allows him to become ethereal and also walk through walls and possess characters. It also gave him the benefits of his old race while living but I told him that was too OP and he can't have the ghost benefits and the racial benefits of a half orc as well.

My question is how does this change my game? What are the implications of going ethereal in Barovia? What does he see lurking in that plane? Obviously he can't escape the demiplane of dread, but what happens when he goes ghost so to speak? Also how will walking through walls mess up the game? How can I essentially keep my game balanced but also let him be a ghost.

Also for background he is a somewhat insane paladin who intends to destroy all evil, although when the party found him he had just destroyed an "evil" bench. He says he is looking for a powerful cleric, it may be funny if that cleric was the Abbot. He'd sense he was a celestial and perhaps even trust him way too much.

Anyway any thoughts on this are appreciated. He's been a very enjoyable addition to the party so far and don't want to crush his creativity but also want to avoid any gamebreaking moments.