Hey guys! I've been trying to work on some homebrew content for an idea of mine, it's gonna be very loosely horror based with plenty of room to goof off, but I also intend to mess around with and test alignments quite a bit with this campaign. I'm already working on a weapon that interacts with the choices the players make while using it (potentially cursing them if they become too evil), but I wondered if you guys had any other ideas on how to mess with or test alignment in a campaign. The thing with the weapon is that it can only really affect one person. I want to figure out a few more ways to mess with the others.
older editions (3rd and older) had tons of rules surrounding alignment and how spells, items, etc. all interacted with characters of various alignments. You could look in to bringing that kind of stuff back, but that's basically been removed in newer editions on purpose.
I'd recommend checking out the AD&D 2E Planescape campaign setting specifically. It's basically THE "alignment matters" setting in D&D history, and just great fun in general imo.