The Four Laws of Undead Physiology

[Greywander]

I've worked on and off for a while now on an undead race for D&D 5e, so I thought it might be fun to codify how I see undead working, which can explain things like why blindfolding a skeleton actually blinds them when they don't have eyes, or whether or not a skeleton is capable of eating and drinking.

1st Law of Undead Physiology - It is extremely difficult for a ghost to physically manifest.

When you think of a ghost, you usually picture that spooky, partially transparent figure that can fly and pass through walls. It is really hard for a ghost to do that, because they're basically creating an entire body out of nothing through sheer force of will. Some ghosts can do it, many cannot. These types of ghosts are rare because they need an especially strong will. This doesn't necessarily make them any more powerful, though, as much of their power goes into simply manifesting in the first place.

2nd Law of Undead Physiology - It is easier for a ghost to physically interact with persons, places, or things that were important or familiar to them in life.

This is often why a ghost haunts a specific location, person, or object. Something to note is that this doesn't just refer to touching or moving things. Sight is also a type of physical interaction; a ghost without a body also does not have eyes, and therefore cannot see unless they manifest eyes. It's easier for a ghost to sense the things that are important or familiar to them than it is to truly see. For example, you could have a ghost who haunts a house it used to live in. Someone buys the house and moves in, and of course they begin moving the furniture around. The ghost is too weak to manifest eyes, so it is actually totally unaware of the new tenant, but it is aware that its things are being moved around, and so moves them back.

3rd Law of Undead Physiology - Undead are fundamentally a ghost possessing a corpse, usually their own.

As per the 1st law, it's often too hard to manifest a totally new body, so as per the 2nd law it's usually easier just to possess your own corpse and use that, if it's available. While in theory the undead spirit should be able to leave their corpse to go elsewhere as a ghost and then return at any time, for unknown reasons a lot of undead spirits seem to bond permanently to their corpses. Perhaps the spirit is simply too weak to manifest apart from their body, and since they spend all of their time in their body, they never grow stronger in that regard.

4th Law of Undead Physiology - If an undead is lacking in body parts or functions, they will manifest what's missing.

A fresh corpse is still mostly functional, so very little is needed on the part of the undead spirit to make it function properly. A skeleton, on the other hand, is missing everything except the basic physical frame. Even so, it's easier for the undead spirit to use the skeleton as scaffolding on which to manifest the most minimal ghostly body they can get away with. The skeleton has no muscles, so the spirit must manifest muscles that will move the skeleton. But only the minimum effort is used, as such the ghostly muscles aren't visible and don't interact with anything except the skeleton. Eyes are manifested in the eye sockets of the skull, but again only a minimal effort is used so the eyes themselves aren't visible. It's a lot more difficult to manifest body parts the creature never had, or to manifest them in an arrangement the creature never had, so manifesting eyes outside of the skull so as to bypass something like a blindfold is often simply too difficult.

A skeleton also needs to manifest an entire speech apparatus, if it intends to speak. This is especially difficult because this manifestation is not just interacting with the skeleton, but with the air which must move to create the speech. Similarly, a skeleton can manifest a stomach to hold food and drink, but such manifestations can be difficult to maintain, particularly if the skeleton does not eat or drink often. As such, skeletons are sometimes "leaky" when they eat or drink, and it varies from skeleton to skeleton. Again, these manifestations are all invisible and interact with nothing except that which they must in order to function.

Anything a ghost could do, a skeleton or rotten zombie could also do, and easier because they don't need to manifest the entire body, only the things that are missing. The force of will required to manifest almost seems to work like muscles that need exercise to become stronger, which might be why each undead always only ever seems to have just enough willpower to manifest exactly what they need. A zombie who gets an arm chopped off won't suddenly manifest a ghostly arm as a replacement, for example, but if they've always been missing parts of their flesh then they will manifest those missing pieces. An undead who begins as a corpse and gradually decays into a skeleton is continually pushing themselves to their limit manifesting each new piece that decays and falls off, until they've built up the willpower to manifest enough to control a skeleton.

Anyway, how do these laws sound? Are there any tweaks you'd make to the wording to make things more clear? Is this how you see undead working in your setting? Let me know.

[JeenLeen]

I think this sounds cool and internally-consistent.
I really, really like the idea about how manifesting takes strength, including, like, eyes to see or it being easier to interact/be seen by those close to you.
I will note that it sounds more like the perspective of an in-world scholar as opposed to the world-designer. Some things are unknown (like if a zombie's ghost is really bound to it or just too weak to do anything else), and that's fine. It gives wiggle-room for the DM and flexibility so you don't create an inconsistency by accident if a certain power doesn't make sense.

Can a ghost abandon a body? This sounds like one of the unknowns. At least, if it can happen, it happens rarely and it's hard to tell the difference between that and the body getting damaged enough to 'destroy' the undead.
Is a ghost hurt by its body being destroyed? I can see it being a shock, since the manifestation via their will is destroyed, and it perhaps destroying (or putting into slumber) the possessing spirit. On the other hand, I can see it just leaving the ghost exhausted and unable to act for a while, but not actually hurt long-term.
Maybe it hurts (most?) ghosts to abandon a body, willingly or due to damage, and that is why they are effectively bound as a skeleton or zombie once they become one: to stop being one would be to destroy oneself, and their will to 'live' is too strong to even consider that option. (If it wasn't that strong, they wouldn't have manifested in the first place.)

Does this make all undead sentient?
Or are some ghosts more-or-less emotional/memory echos of their past selves, instead of a true person. Mainly this is asking if your Laws allow for non-sentient undead, like mindless skeletons and zombies.
On the other hand, the end result might be minor. Just most dungeons of "mindless undead" are actually minded undead, but they are focused on the violence with which they died, or protecting the dungeon they guarded in life, so they act aggressive to anything that comes there.

What does this mean for magic? You mention 5e.
I can see spells like Create Undead and such help the ghost by empowering it with the magical energy, thereby making the manifestation easier. Perhaps in exchange the magic binds the spirit to the corpse, and the will to the creator of the undead.
Turn/Rebuke Undead powers overwhelm and channel the will of the undead, linking it to the user. (I forget how Turn works in 5e, but in 3.5 it had a chance to make them flee or destroy them.) If flee, it turns their focus to 'run away'; if destroy, it forces their will away from manifesting so that the possession fails, and the possessor (if not destroyed by that trauma--see earlier question) runs away.

[Quizatzhaderac]

In my opinion, vampires and werewolves are a bad match for D&D's definition of undead. They're unnaturally vital, as opposed to being unnatural unvital like the rest of the undead. In your case, they also raise complex questions about the spirit is unnaturally attached to a complete body.

I think a better fit would be aberrations. Some new thing grows and replaces the body. In the case of werewolves in only replaces the body temporarily. In the case of vampires, its mind grows in the memories of the dead person, thus creating a superficially similar mind.

Which is also (I think) how mind flayers work. A mindflayer larva is planted in the neck of a victim and it grows to replace the victim's head.

The sprit grows attachments in life
A typical living person's spirit and body are strongly attached. This weakens after time and especially after a proper burial. Eventually the separation is complete enough that a spirit can move on to the afterlife.

Mummies are a special case as the funeral process is designed to preserve the spirit's attachment to the flesh rather than to ease the separation.

A person's spirit is also naturally attached (to a degree) to the people and things that are important to it. The typical person that becomes a ghost is obsessively attached to something.

Thinking requires and articulately manifested brain
The typical undead are doing something akin to sleepwalking. Within seconds of death (and often even before) the brain is badly damaged.

A sapient undead requires extra effort be spent to supplement/replace the damaged brain. A typical lich's phylactery is a complex item that the lich crafts and attaches themself to while still alive.

[sktarq]

Main question is
what type of undead need to be supported by these laws?

leaning toward classic D&D undead just as a model.
because if you have shadows, wraiths, etc they need a way to be separated from "normal" ghosts
do you have sentient vs non-sentient undead and how would that work? for corporeal and noncorporeal undead.
How about spawn type undead? how would that work...why
why do some undead drain stats or levels and others don't?

now this may also not be for a D&D setting for sure but the same kind of questions would need to be asked in order to understand the type and variety of undead in the setting. To some extent you need to take your monster manual/story needs and work backwards.

[Greywander]

Does this make all undead sentient?
Or are some ghosts more-or-less emotional/memory echos of their past selves, instead of a true person. Mainly this is asking if your Laws allow for non-sentient undead, like mindless skeletons and zombies.

because if you have shadows, wraiths, etc they need a way to be separated from "normal" ghosts
do you have sentient vs non-sentient undead and how would that work? for corporeal and noncorporeal undead.

There could exist a variety of spirits (undead or otherwise) aside from that of a dead person that could be used to animate a corpse, some of which would not be fully sentient. There might even exist "native" undead spirits, i.e. spirits that have always been undead and were never alive in the first place. Such spirits might have their own special properties, allowing them to possess the corpse of a creature even if it's not someone they're familiar with.

D&D also makes a distinction between a soul and an animating spirit, so we could also draw on that. IIRC, the animating spirit is what actually moves the body, and it holds all the memories, but it isn't capable of acting intelligently or learning new information. Most mindless undead have an animating spirit but not a soul. Often they'll mimic the routines they had in life, even when those routines stop making sense (e.g. miming sweeping motions with a broken broom handle with no broom head). They seem to also respond instinctively to the presence of the living by attacking them.

The echo ghost could be another interesting thing to explore, and it would probably have some unique properties of its own. Perhaps they're created by spiritual residue left behind by the dead person, both as a result of their death, but also just by interacting with things while alive. Once they're dead, that spiritual residue might conjure up the memory of that person as a ghost, but the ghost itself isn't really real. The ghost isn't intelligent, per se, but acts according to how that person was remembered by that place or those objects (or some other person that holds a large amount of the dead person's spiritual residue). Over time, such spiritual residue might fade away, or could be cleansed by a priest.

How about spawn type undead? how would that work...why
why do some undead drain stats or levels and others don't?

Different undead have different specific powers. Often it's a question of how the undead was created in the first place, as the method of creation can imbue the undead with specific traits. Some creatures are "native" undead, as in they were never alive, and like any other monster they have their own unique traits.

What does this mean for magic? You mention 5e.
I can see spells like Create Undead and such help the ghost by empowering it with the magical energy, thereby making the manifestation easier. Perhaps in exchange the magic binds the spirit to the corpse, and the will to the creator of the undead.
Turn/Rebuke Undead powers overwhelm and channel the will of the undead, linking it to the user. (I forget how Turn works in 5e, but in 3.5 it had a chance to make them flee or destroy them.) If flee, it turns their focus to 'run away'; if destroy, it forces their will away from manifesting so that the possession fails, and the possessor (if not destroyed by that trauma--see earlier question) runs away.

Most magic that creates undead probably works by either calling up the dead person's soul and binding it to their dead body, calling up the person's animating spirit and commanding it to move the body again, or calling up some other kind of spirit to inhabit the body. The magic might supply some of the energy needed to manifest missing or nonfunctional parts of the body, and as this magic fades the spirit will grow gradually stronger in order to take over that burden.

Turn Undead in 5e initially just makes them flee, but as you level up it will automatically destroy weaker undead (it's considered a weak feature, as you get it too late and it only destroys really weak undead). Perhaps Turn Undead creates a pulse of positive energy that disrupts the ability of ghosts to manifest, triggering a primal reaction wherein they feel as though they must flee or be destroyed. The pulse isn't actually that powerful, but it's enough to trigger that primal fear.

In my opinion, vampires and werewolves are a bad match for D&D's definition of undead. They're unnaturally vital, as opposed to being unnatural unvital like the rest of the undead. In your case, they also raise complex questions about the spirit is unnaturally attached to a complete body.

I don't actually know that werewolves are considered undead all that often, and not in D&D. Werewolves are more part of the "monster mash", a collection of Halloween-themed monsters that does include some undead, like vampires and mummies, as well as Frankenstein's monster (which is either undead or a construct), as well as some non-undead monsters. Anyway, I'm not considering werewolves to be undead.

For vampires, there's usually some kind of powerful magic or curse involved, so that can explain why they're unnaturally full of life for an undead. The same magic that causes them to disintegrate in sunlight or running water, or that forbids them from entering a home without being invited, or that causes them to become paralyzed when staked through the heart, etc., also allows them to appear as nearly alive, or turn into a cloud of mist or swarm of bats, or climb up walls, etc.

The sprit grows attachments in life
A typical living person's spirit and body are strongly attached. This weakens after time and especially after a proper burial. Eventually the separation is complete enough that a spirit can move on to the afterlife.

This could be an interesting thing to explore, why some people die and go to the afterlife while others linger and haunt the living. For undead created by magic, the attachment can be enforced and made permanent, so that no amount of time passing will weaken it, until the undead creature dies again. Generally I would assume that most of those who die go immediately to the afterlife, so those who stick around are probably pretty rare and might not be as well understood as the undead that are created with magic.

Thinking requires and articulately manifested brain
The typical undead are doing something akin to sleepwalking. Within seconds of death (and often even before) the brain is badly damaged.

A sapient undead requires extra effort be spent to supplement/replace the damaged brain. A typical lich's phylactery is a complex item that the lich crafts and attaches themself to while still alive.

I actually didn't think about this, but it does make sense. A functional brain is probably something that all undead have to manifest, albeit the fresher their corpse is the less work they need to "repair" their brain. A ghost that can't manifest a brain would be extremely limited in what it could do, and might cease to exist altogether. Those that can only manage a partial manifestation might be limited to more instinctual actions typically associated with mindless undead.

[Quizatzhaderac]

For vampires, there's usually some kind of powerful magic or curse involved, so that can explain why they're unnaturally full of life for an undead.

From my point of view, it's not so much a detail that needs explaining, but direct contradiction. "why is that blindfold polkadot?" versus "That's see through, and therefore not a blindfold."

Also, it would make sense for me if a vampire could be poisoned by garlic, but D&D undead don't have constitution scores, so all of those mechanics are out of the window.

Generally I would assume that most of those who die go immediately to the afterlife, so those who stick around are probably pretty rare and might not be as well understood as the undead that are created with magic.

So I was kind of imagining the default it that the spirit is still stuck in the body until the funeral and during the first stages of the survivors' grief. This has two effects:

Funerals ceremonies are a practical matter, not pure sentimentality. This supports a magical thinking mindset (if that's desirable) as opposed to magic just being science in robes.

It explains that spirits are still around, so a necromancer can still make a zombie from a fresh grave (if not an old one); and doesn't need a living person or an exceptional dead person to make a zombie.

A ghost that can't manifest a brain would be extremely limited in what it could do, and might cease to exist altogether.

For ghosts specifically, the limits could be very asymmetric. Like, they retain the ability to plan revenge on their child's killer, but lose the ability consider that they endanger their surviving children in the process.

[Greywander]

Also, it would make sense for me if a vampire could be poisoned by garlic, but D&D undead don't have constitution scores, so all of those mechanics are out of the window.

This is edition specific. In 5e, undead have Constitution scores, and vampires are IIRC the only undead we have so far that are not immune to poison. Interestingly, apparently none of the monsters in 5e are immune to disease, but I'm not sure if this is an oversight or if it's intentional.

On the subject of undead and Constitution, when thinking about, say, what kind of check would be needed for a skeleton to keep food or drink contained, a CON check is what makes sense to me. In general, CON could take on a new meaning for undead, where it represents how well they can physically manifest (compared to their current state, not compared to each other, e.g. a ghost is always better at manifesting than a zombie is, even with a lower CON score). The better they are at manifesting, the more functional their body becomes, and thus the more "lively" they are. The end result isn't so different from a living person who is in particularly good health, which is what CON normally represents.