Doppelganger [Ravenloft]

In its true form this doppelganger is a sexless biped with a hideous face: hairless, ash-gray head, pointed ears that jut outward, a gap of several inches between nose and mouth, and eyes set far too high. Its thick, folded hide gives it a natural AC of 5, and it has no nails on fingers or toes. Creases under the eyes reveal its age; more creases mean an older creature. It reverts to this face at death, sometimes flickering through recent stolen forms first if it dies slowly.

It can become any humanoid four to eight feet tall. It kills a lone victim, takes its shape and joins the victim's companions. Sleep and charm do not affect it; its saves are those of a 10th-level fighter.

Unlike common doppelgangers, which copy at only 90% accuracy, this kind produces a form that is real even to the touch. Changing takes a full round, and it gains none of the copied body's abilities; it could look heavily muscled without being any stronger. To copy someone well it must see them clearly, usually within 30 feet; poor light shortens that, while scrying magic, or even a good spyglass, extends it.

It can reshape carried gear into other items of similar purpose and material, turning an axe into a sword or rags into a gown or leather armor, but never cloth into plate. Altered items work like what they now are, but revert if more than 5 feet from the creature. So it carries a bit of everything, from plain clothes and a medium metal weapon to knives, tools and small carved wooden things, though it prefers real items and always strips its victims.

Its ESP matches the spell but has no usage limit, so the DM need roll saves for the PCs only when timing matters; eventually they fail. It reads a group to pick the best victim and moment, studies that victim's mind for days before the kill, then reads everyone nearby to act as expected. It is never surprised and rarely slips. Its weak point is skills it cannot copy, like spellcasting, high-level thieving or special proficiencies, and it uses ESP to dodge such demands.

Clans of three to twelve, without children, follow a pecking order under the eldest. On a job, the youngest take the riskiest tasks and lowest-status victims, while the leader replaces the most important target. Once one member is inside, it helps the others claim more victims. They work upward: a guard or servant, then the guard captain or chief steward, then a family member, and finally the noble.

They avoid victims whose lives depend on skills or unique talents, wizards most of all. They can learn thieving skills up to the level of a 7th-level thief, but only for use in the form in which they were learned. Even so, they rarely replace thieves, preferring law-abiding citizens. Being sexless, they often flout the gender roles of a borrowed body, conforming only when survival demands it.

Greedy cowards, they target the rich, squander the loot and flee real danger, rarely risking a comfortable new identity.

Their greatest limitation is that they cannot breed with each other, only with other humanoids, imitating whichever sex is needed. The doppelganger blood always dominates, yet the child looks like a normal member of the other parent's race until puberty, when it slowly shifts toward the true doppelganger form. Then a clan member, ideally the doppelganger parent if it is still posing as a spouse, reveals the truth. With a dozen or more years between conception and that moment, the parent may be unmasked, driven off or dead by then, leaving another clan member to try, not always successfully. A child who never learns its heritage is likely to be discovered and killed.