Okay, gotta say that's actually a really cool ability. Him having the pill is a good idea, and if something happens to it before he needs to take it, they can all improvise if it becomes necessary/other characters know it's a thing/whatever.

As a whole, I think he's definitely going to be a great asset; they can't have too many people who know how to fight, and his experience dealing with the supernatural/hauntings is doing to super helpful.

As far as what direction you should take, I think you should go with whatever will be most fun for you, as either will be useful, and both would be fun to play off of.

I'm pretty chill as far as plotting goes, too, but I'm going to see if I can't brainstorm a few ideas together so as a whole we can decide what direction we want to take the mission (and hopefully other people will have ideas/contributions to bring tot he table, too!) ICly, I think I'll probably put a network post up later this week so characters have a way to learn about it and whatnot.