As anyone who's played the games will know, family bloodlines can end up getting a little weird in Crusader Kings - so why not add vampirism and lycanthropy to the mix?
Princes of Darkness is an overhaul mod based on the World of Darkness universe (the setting for Vampire: The Masquerade), and brings some good old Transyvlanian energy to the medieval world of Crusader Kings 3. It's made by the same team who completed its predecessor mod for Crusader Kings 2, and judging by the sheer complexity of this one, it's clear the team has some experience.
I'm not fully up to speed on World of Darkness lore, but I dipped my toe into the mod and still managed to keep up - as much as I usually can in Crusader Kings, anyway. The important thing is you're a vampire, and therefore practically immortal: regular causes of death like disease won't end your life, but you can still be torched or decapitated. More worryingly, failing to manage your stress levels (known as "The Beast") will cause you to transform into a feral wight, resulting in your character's abdication. Oh, and everyone will hate you.