EDIT April 2018: Check out my updated take on this alongside some neat ways to change up Tomb of Annihilation (again) here!
Sometimes, the sweet embrace of death is all but impossible for countless damned souls. They are forced to continue to walk a dark path. For them, they seek to regain an essence of life and restore their shattered minds, lest they be lost to an abyss of emptiness and madness. Such a curse can be from a variety of sources; an exploitation of a life source at a deific level, exposure to/using evil magics for too long, a hex brought upon by a powerful caster or even a destructive force bent on draining life from all reality.
The Curse of Undeath is a vile magical power that breaks the soul and leaves the body as little more than a husk. These drained husks share little with their once living counterparts. They are merely corpses controlled and warped by dread energy. Any remnants of mind left in these creatures are stretched to madness and driven to violence. While many of them retain enough knowledge to fight as though could in life, it is impossible for them to engage in rational dialogue let alone interact peacefully.
Author’s Note: Dark Souls III is out and I love it! With that, here’s an optional rule for handling a curse similar to the Undead of the Dark Souls universe. If you don’t want to literally be running Dark Souls, it shouldn’t be too hard to reflavor this into a different dread curse of sorts. If you’ve ever played Eternal Darkness: Sanity’s Requiem, Anthony’s chapter certainly comes to mind. One last disclaimer, these are mostly random ideas in my head, in an attempt to make a Dark Souls inspired mechanic. As such, it’s more than likely that this idea is a bit clunky. It will probably receive a revision in the future, if reader interest is there.
An Affliction of Body, Mind and Soul
As the last of life’s flames extinguish, you become less and less human. For every time you die, a piece of you is lost when you’re brought back. Only through restoring your humanity can you truly become whole. Even before the curse has truly taken hold of you, its dark power has tainted you indefinitely. You may currently look like one of the living, but heinous power seeks to transform you into one of many mindless and angry dead.
The source of the curse can be from one of several horrible events. Perhaps the Gods attempted to prolong the life of themselves and their followers by draining life essence from the planes. Perhaps an entire area was desecrated by overuse of necromancy. No matter the cause, the results will turn apocalyptic in the long run as people without souls begin to wither into deranged husks. Even before before truly becoming one of the Undead, the cursed already suffer greatly. Upon being afflicted by the Curse of Undeath, you automatically fail death saving throws when brought to 0 HP. You must still roll a Death save. Upon failure, you receive two failed saves instead. Getting a natural 1 causes three failed saves instead of two.
Using Purity as the Curse.
Using this system, you can replace the incremental levels of corruption with levels of undeath instead. Every time you die, you lose an amount of purity and take on a level of the curse. In this case, the stat is renamed Humanity (or some other name, if your game isn’t human-centric.) When you die, you lose 1d4 Humanity. If you go beyond an increment level, you gain an aspect of the Curse.
If you are at the Mild Corruption level, you begin to look very sickly and unhealthy. At Moderate Corruption level, you clearly look like an undead creature. At Severe Corruption, you look exactly like a Hollowed Out Creature. However, you still have most of your mental functions and rationality in tact… for now. Upon dropping to 0 Purity, you are a Hollowed Out NPC and effectively a monster.
Otherwise, this is a particularly cruel effect on the Corruption Charts.
This method is inspired by Ravenloft, where you must make a Powers Check to avoid corruption. Upon death, you must roll a d100 to see if you become tainted by Undeath. If your roll is equal to or lower than your Undeath taint score, you become a Hollowed Out Creature (NPC Zombie). In order to count up your current corruption level, you roll a d10 at the time of your death. You add the roll to your current corruption level. Even if you succeed in revival, you look more and more like the Living Dead with every reanimation. Upon gaining even a little corruption, you gain the first stage of undeath. Upon going beyond 33%, you gain the second stage. Upon going beyond 66%, you gain the third stage.
Regaining Your Soul.
In order to reclaim lost life, you must return to the scene of your death. With the lost essence retrieved, you must then meditate in a safe haven. Safe Havens are places with radiant fire. This can manifest as a burning shrub, a bonfire, a celestial symbol or the like. By taking a short or long rest after you’ve reclaimed your lost soul, you are restored back to your previous state. Furthermore, upon dying, you are transported back to a Safe Haven mere moments later.
Another method is by killing enemies and taking aspects of their life energy. More powerful creatures give larger amounts of energy. Smaller and normal creatures do not give off life energy that you are able to steal. Larger creatures typically give 1, while incredible creatures give between 5 – 10. This energy can be use to regain your original mortal state. Depending on the above system that you’re using, you can spend this life energy to recover. For the first system, you can recover 1d4 Purity after spending 20 of your life energy points. For the second system, you can regain up to 2d10 on the power check scale.
Beyond this, you must be active in the world and not give into despair. Those who give up on life quickly become hollowed out. By engaging others and doing what you can to retain your life essence, you can stave off the curse’s effects. In fact, you can harvest life essence from slain creatures and use it to regain your true form at a radiant fire.
If neither of the above options are appealing, you can just have increments of corruption (as listed below) before the character becomes an undead NPC.
Becoming the Undead.
When you lose your life essence, it saps away at the fabric of your being.
When you become afflicted with an undead status, you gain the following properties: You have resistance against poison damage and advantage against poison effects. You do not need to eat or breath. Sleep is only needed to regain abilities and maintain humanity, you can meditate for the amount of time you normally sleep. You lose 1d10 maximum hit points until restored.*
As your descent into soulless undeath continues, you gain more qualities: You gain resistance to Necrotic damage and have immunity to Poison damage, but gain weakness to Radiant and Fire damage. You are immune to poison effects and disease. You have resistance to magical healing. You lose another 1d10 maximum hit points until restored.*
When you become hollowed out, you gain the following effects: You lose proficiency in all checks, including saving throws, as your grip on life has all but faded into oblivion. However, you remain proficient in attacking. You are immune to charm and fear effects as well as magical healing. You lose another 1d10 maximum hit points until restored.*
*If your maximum HP drops to 0, you become a Hollowed Out NPC and regain all of your previously lost hit points.
Image Source: Revenant – oevrlord
Based off of Dark Souls, which belongs to From Software. Made by Doctor Necrotic, for Doctor Necrotic Media.