As with all comforting tales, this is not the case in reality. The truth is far stranger.
We know nothing of where they come from. The most common belief is that they come from some other world, though one not like ours. It is believed that this is the same world that other oddities come from, but this unsure. The Doppelgangers themselves are reluctant to speak of their origins, or of their past in general. They loathe not just their own origin, but anything that distracts them from the current moment. They care nothing that might remind them of their past, for that is nothing but a wound in of itself. Sometimes they carry small mementos with them, but eventually even these precious memories drain away, and the Doppelganger is left holding some small, insignificant treasure, mourning something they didn't know they had.
For Doppelgangers can never remember what they are supposed to be.
It always starts the same. The Doppelganger attacks someone, or comes across a freshly slain corpse. It feasts on the corpse, but most importantly, it cuts open the head of the person and eats their brain. This allows it to absorb the corpse's memories. For a little while, the Doppelganger is that person. If your wife died and a Doppelganger ate her brain, for a while, she would essentially be your wife, in terms of memories, personality and appearance. She would know everything your wife would, and feel the same as your wife did when she did. If she loved you, so will the Doppelganger.
But then, slowly, things change. First the Doppelganger begins to forget unessential things that your wife knew. When was your anniversary was, or what her favorite type of wine was. Then her memory loss accelerates. The Doppelganger will soon find it difficult to recall even basic facts about your wife, and eventually, you will realize that this thing is not actually your wife. It is something else, impersonating her.
The Doppelgangers know this. Some try to stave off this inevitable memory loss with rhyming tricks, memorization techniques and other such things. Others merely skip town the second they can't remember what "their" brother's name is. Either way, this wounds the Doppelganger. They feel just like the person whose brain they devoured. Even as they tell themselves that what they feel can't be real, they still feel it, and the heart is much more persuasive than the head.
Sometimes it doesn't last that long though. Sometimes the husband finds his wife's corpse, especially if the Doppelganger did a poor job of disposing of it. Sometimes he assumes the Doppelganger did the deed, and kills it. Sometimes the Doppelganger even did do it. How the Doppelganger reacts is always different. If the Doppelganger is hardened by years of this, and the wife was not particularly fond of her husband, or the Doppelganger has already forgotten most of what it "remembers" about the husband, it may just kill him. On the other hand, it may still feel some sort of love for this man, and may simply flee, or even try to explain itself. This rarely goes well.
Other Doppelgangers find this whole cycle too depressing. They reject brain-eating and the consumption of other's memories, and instead try to live their own lives. They use their Shape-shifting powers not to impersonate others but to craft elaborate personas for themselves. They borrow a nose from the beautiful man next door, the hair of the maiden who ruled the hearts of the village where they grew up, and the King's shapely chin to become their own person. They attempt to create their own memories and reject their own alien nature.
This doesn't usually work either. Though the Doppelganger is usually spared the negative effects with this path. For upon death, a Doppelganger reverts to their previous form, a hideous, alien freak. This reveals the deception, and often scars all of those involved.
For this reason and for others, most people who know they exist hate Doppelgangers.
Fear of the Other
We don't understand Doppelgangers, and even if you do, they are still strange and odd. The idea that your loved one was actually a shape-shifting monster, it is scary. People are burned not just for illegal magic or necromancy, some are accused of being Doppelgangers and beaten with axe handles until they confess to being a "skin-wearing devil", then are dragged off to be burned. Very few of those killed like this revert to being a Doppelganger upon death.
However, these victims being killed by a mob rarely calm things down. This usually just leads to more blood, more corpses and more innocents fed to the flames. Discovering someone you knew, especially if they might have killed the "real" version of that person, is a monster can cause a lot of stress and anxiety. But the idea that anyone around you could actually be a Doppelganger, that is enough to make you never trust anyone ever again.
Doppelgangers are not from our world. They do not obey our laws, but like a citizen of a wealthy and powerful nation, carry their privileges with them like an invisible force-field. This subtly warps the fabric of reality. For one Doppelganger, this effect is minor, and barely noticeable. A large group on the other hand, is all but impossible to not notice.
How their Distortion works is this: they cause objects to change shape. Your sword suddenly changes into a feather-duster. It feels like a feather duster to you, weighs as much as one, and looks like on. It still possesses the same qualities, not that you might realize this. This means that areas around Doppelgangers are slightly weird, and Dungeons full of them are madhouses, where Goblins attack with mops and brooms and hurl jack-o-lanterns, and Ogres dressed in ball gowns and rainbow silks throw glittering chandeliers at Fighting Men clad in pajamas and wielding pillows and an enormous stuffed bear. This Distortion never affects people.
These aren't hallucinations, by the way. They look and feel real to everyone, and only a magic spell can reveal the truth. The distortion ends if the Doppelganger dies or either of you get more than 1 miles away. This is how a Fighter can be standing over the corpse of a Doppelganger, panting after a hard fight, only to realize that instead of their magic sword, they are actually holding a broken broom handle dripping translucent viscera.
Doppelgangers don't have a society. Their seems to be no kinship between them, and they seem to work independently of each other. There is no Doppelganger society. There is certainly no secret Doppelganger order bent on controlling our world through subversive means. That would be crazy.
Entering the Doppelganger Conspiracy: You encounter a Doppelganger or see one revealed. If the Doppelganger is in disguise, it doesn't count.
Aware: You are now aware that Doppelgangers exist. You develop a new caution bordering on paranoia. Anyone around you could be a Doppelganger. The Referee should call for you to roll on the Doppelganger Encounter Table whenever you are in the presence of a Doppelganger (disguised or otherwise).
Note for the Referee: Each session has a 3-in-6 chance of the afflicted being near a Doppelganger. However, there is also a 2-in-6 chance that this is a false alarm.
Involved: You are now aware that the Doppelgangers are working together. They want something. You trust less and less. Strangers could be spies, presents could be traps, invitations could be snares meant for something. Nothing is at it seems. The Referee should call for you to roll on the Doppelganger Encounter Table at least once a session.
Collaborating: The Doppelgangers are not just working together with each other, you now realize. They have friends, other people who are not Doppelgangers working for them as well. You trust nothing now. Even close friends are suspected. You see conspiracy in every side-long glance, and daggers in the dark haunt your dreams. The Referee should call for you to roll on the Doppelganger Encounter Table at least twice a session.
The Doppelganger Encounter Table
1- One person here is secretly a Doppelganger. You saw them transform when they thought no one could see them.
2- One person here is secretly lying about something.
3- Two people here are lying about their relationship. They may be allies when pretending to be enemies, hate each other when pretending to be lovers, etc.
4- One supposedly good thing is actually a trap.
5- One seeming trap is actually a double-bluff, it hopes you think it is a trap so you won't try and use it.
6- One enemy here is actually also aware of the Doppelganger conspiracy, and could be recruited if you told them about your secret knowledge.
7- You become aware of the fact that someone is secretly observing you right now.
8- One ally here is plotting something. Their smile seems a bit forced, and you swear you saw them conceal a knife in their boot.
9- You find a sign that indicates a Doppelganger was near your location. Examples include but are not limited to mysterious corpses, footprints, human brains left lying around, the fact that your helmet now looks like a coonskin cap, etc.
10- One object you possess changes to look like something else. It still keeps its same properties, but you don't know that. This has a 2-in-6 chance of being a "False Alarm" and no Doppelgangers are actually within range.
11- The next person who dies, no matter who they are, transforms into a Doppelganger upon death.
12- You suddenly encounter yourself. This other version claims it is the real version, and that you are actually a Doppelganger. You have a 50% chance of secretly being a Doppelganger, and this version of you being the "real one", and vice versa. Additionally, if you roll this option, advance one stage in the Doppelganger Conspiracy and increase the amount of times you roll on the Doppelganger Encounter Table by 1. If you are already at Stage 3, you instead become a Doppelganger and start forgetting everything about who you once were. Now, instead roll on the Descent of the Doppelganger table whenever you would roll on the Doppelganger Encounter table.
For the Descent of the Doppelganger table, roll 1dX, and add +1 for each previous time you've rolled on the table. When you reach 10+, you have forgotten everything.
Descent of the Doppelganger
1: You forget your place of origin
2: You forget some minor fact about yourself (favorite food, color, song, myth, etc)
3: You forget some minor person from your past
4: You forget a trinket or other unimportant possession
5: You forget an important someone's name
6: You forget a very important person from your past
7: You forget what your goal is. If you didn't have a clear goal before, you suddenly get one, as you were sure you had one up until now.
8: You forget some of what you know about a skill (lose access to a class level)
9: You forget what your face looks like- it slowly begins to change over the course of a few days, until you look like someone totally different
10: You forget your own name.
11+: You forget everything about who you once were. You know nothing of what you were. Your character becomes an NPC Doppelganger, under the control of the Referee.
Nuts and Bolts
HD 2 AC 14 Atk as Weapon
Mor 8 Saves 9 or less is a success
Shape-shifter: Doppelgangers can change themselves to look like any type of medium or small Humanoid. Their stats do not change, no matter how they look.
Brain Eater: If a Doppelganger eats someone's brain, they can absorb their memories and personality. For a time, they are that person, in all but technicality. But soon they forget, and return to as they were before.
Sneaky: Doppelgangers are very sneaky. They get +4 to all stealth rolls, and +4 to attack rolls during surprise rounds.
Distortion: As long as they are within 1 mile, Doppelgangers cause objects to change their shape. This doesn't change their actual properties, but they look and feel like something else. Ex: A sword that looks like a feather duster looks and feels like a feather duster, yet it can still cut you. A skull that looks like a pillow will cold, dry and hard, no matter how nice it looks. These Distortions last until the Doppelganger dies or one of you gets far enough away.
- Impersonate someone
- Lie effortlessly
- But is it a lie if I believe it?
- Run if confronted with serious resistance
Doppelganger Encounters/Plot Hooks:
1- In a dungeon, a Doppelganger waits for a player to wander off alone, or lures them away, then beats them up and throws them down a chute or off a cliff down to a lower level. Then it pretends to be that player.
2- If you left a body behind, a Doppelganger finds the corpse, eats its brain, and dresses itself in the corpse's clothes. They come back to you and pretend to be that person.
3- A Doppelganger approaches the players as someone they do not know and tries to befriend them. It wants to manipulate them for some sinister purpose, probably. Or maybe they just want to be loved. Who knows?
4- A village hires the PCs to investigate a missing girl. However, just a little while into their search, the PCs find the girl. However, she seems odd and not quite normal. Is she a Doppelganger, or just confused?
5- As you enter a village, you see everyone crowded around the courthouse. Apparently, a local has been accused of being a Doppelganger and is being tried. The evidence is ridiculous and laughable, but the whole town has been worked up into such a frenzy that this seems reasonable. You might be able to talk them down, or you might be accused of being a Doppelganger yourself.
6- When the players return to a certain place they have already been, one of them is accused of committing various crimes. This is because unbeknownst to them, a Doppelganger stalks the players for a certain amount of time. Then it returned to this place to do crimes, using the PC's face as a mask.
7- A small group of Doppelgangers is working to take over a small city. They have stable identities not based on brain-eating, and use their brain-eating and stealth skills to eliminate any challenge to their rule. They know everything, and since they know everyone's secrets, no one dares moves against them.
8- A city recently discovered a Doppelganger in their midst, and is currently tearing itself apart as it searches for the rest of them. Armed inspectors are going door to door, interrogating any strangers, ethnic minorities, or practicioner of small, possibly heretical sects. The whole city is perched on the edge of violence, and one spark could ignite the powder keg and plunge the whole city into open revolt.