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.
Obviously, you'll also need to keep an eye on your hunger, "a core modifier representing your need for blood". This is what helps fuel your special vampire schemes and powers, and can be replenished slowly over time or with active hunting. Just as well you can alter contracts to demand blood tithes from your vassals, eh?
From poking around the mod, I found that vampirism grants you access to a bunch of cool new skills like blood sorcery, many of which can be unlocked using special spooky lifestyle trees named after the humours. Intrigue plays a larger role than normal in this mod, and I tested it out by immediately sending my buddies off to steal the soul of a neighbouring king. I'm hoping to stake a claim on his territory soon.
Religion is also hugely important in this mod, with different strains of vampirism adhering to different codes, and all of them seemingly hating each other. Warfare, meanwhile, places a heavier emphasis on knights, with the prowess of your knights allowing you to overcome more numerous forces - "especially if mostly composed of levies". I get the feeling the peasants are really not going to have a good time in this one, particularly given you can control them through buildings in your cities as a vampire overlord.