They start as bones — it always starts with bones. Set to guard. Mindless.
The mold and dust and detritus of a dark dungeon hall will coalesce in layers like organic sentiment. Given enough time, this mess begins to resemble flesh once more. The bones cloak themselves from the bludgeoning damage of the priest.
Their flesh regained, the bones will soon remember what it is to hunger. As they feed on the living, they digest glimpses of wit and develop a meager cunning. The concoction of flesh and bone and sentience begins to leech magic into the creature’s fangs and claws; the claws can paralyze and the teeth make the condition contagious. In the strongest specimens, these foul humors become volatile and waft off in sickening vapors.
By this point in its development, the creature’s appetite reaches beyond the physical. It has ingested enough flesh memories to remember what it is to experience. The void opened by its hunger will siphon an enemy’s lived experience and memory. It’s a zero sum game — a creature slain by this effect will rise as its own void of knowledge.
Once the bones get a taste for sapience, they are gripped with fear. They remember what it was to be vulnerable first as brittle tomb guards and later as flesh-clothed hunters. They cannot abide this weakness, and abandon the physical entirely. They are only void, still feeding on the experience of living creatures but now without the weaknesses that flesh incurs.
The next stages are cyclical. The creature cannot abandon the flesh, much as it tries. Almost inevitably, strips of cloth collect on its form — a scrap of bandage, a torn banner. The void is encased in a cocoon of linen from which it wants nothing more than to escape. The void within it is seemingly staunched by the cloths, and the creature loses its ability to steal experiences. But it always breaks free again, ever more resentful.
The creature’s penultimate form is one of paradoxes. It appears physical, but it casts no shadow. It feeds not on memories but on blood. It regains a humanoid appearance, but retains its immunity to non-magical weaponry. The seemingly random assortment of garlic, holy symbols, mirrors, wooden stakes, sunlight, fire, and running water are some of its few weaknesses. It vaguely remembers what it is to be a participant in society and won’t enter a building uninvited. This creature’s diet of blood gives it a connection to the world of the living. It often commands packs of rats, bats, and wolves and can even assume their forms.
For many bones, this is the final stop. But a rare few grow weary of this “life” and abandon their holdings and castles and schemes. They ascend to a purer, cleaner form. Once again the creature is liberated from the weaknesses of the flesh. It no longer drains experience but instead annihilates a creature’s life force entirely. A single look can send weaker beings fleeing in terror. The creature can interface with matter at a direct, raw level. It can seize control of a living creature’s body or even manipulate objects around it.
The undead are many and varied.
But it always starts with bones.
It’s a long web of credits for this exercise — I got the idea from Prismatic Wasteland’s Wizards Playing Telephone, who in turn credits Save Vs Die who in turn credits Grognardia. I also read Semper Initiativus Unum’s OD&D Setting.
This undead ecology takes the Turn Undead table from Basic Fantasy (which is just like the OD&D one but with Ghost added at the top) and assumes it’s a life cycle rather than an increasingly powerful list of unrelated creatures.