I do not find Doppelgangers that interesting. It isn’t that they’re terrible, it is that their use is either mostly off-screen in the form of replacing NPCs and causing havoc with social connections, or they are used as a surprise source of conflict, taking the form of some familiar or new face so that they can lure a lone PC away to try and murder them. These aren’t necessarily bad encounters, but rather they’re fairly one-note. Ultimately they rely on effectively ambushing and hiding from the PCs, revealing themselves only when absolutely necessary.
My main issue is that ultimately once they are revealed, they lose most of their efficacy as a threat. There’s also the simple fact that attacks against player cultivated NPCs tends to lead to either murder-hobos, or to PCs who always, tragically, have no living loved ones left. But this is really dancing around a greater point, they are just not that physically imposing. They are only consistently capable of killing PCs who have been separated from the group, and even then, only characters not specialized in fighting. I have included statistics for both the AD&D and the 5th Edition Doppelganger below.
FREQUENCY: Very rare
NO. APPEARING: 3- 12
ARMOR CLASS: 5
HIT DICE: 4
% IN LAIR: 20%
TREASURE TYPE: E
NO. OF ATTACKS: 1
SPECIAL ATTACKS: Surprise on a 1-4
SPECIAL DEFENSES: See below
MAGIC RESISTANCE: See below
PSlONlC ABILITY: Nil
Attack/Defense Modes: Nil
Dopplegangers are able to ESP and imitate with 90% accuracy. They are subject to neither sleep nor charm spells. Despite having only 4 hit dice they make all saving throws as if they were 10th level fighting men
5th Edition Doppelganger
Who Goes There?, The Thing From Another World & The Thing, as well as two episodes of the X-Files, Ice and Firewalker, are all horror works based a simple premise: An alien is found in an isolated environment. It either has the ability to either cloak itself as a human, or is able to infect/convert them into more of itself. The alien can work as a group of autonomous beings, or as a single entity that unifies together for tasks requiring brute force.
These works have an advantage over typical Doppelganger tales in that they are in a secluded and generally extreme environment. Social mysteries are difficult to write for D&D, doubly so for ones like Doppelgangers demand, rife with social cues and deceptions. Instead of a familiar setting, the Thing works best in a crowd of strangers, some of whom will need to help and trust the PCs if they are going to have a chance of survival against it. Unlike a Doppelganger, the Thing isn’t a single creature, and any part of it can continue to survive and infect others until it grows back into a threat once more. While it has a ‘natural’ form, there’s no reason to ever reveal it to the players.
B/X and LotFP Stats
HD: Variable, see Special
Move: 30’, 30’ Climb, 30’ Swim.
Attacks: Variable, see Special
Special: Things begins with 3 HD, and only 1 attack at 1d12. An attack resulting in the victim’s death gains the Thing an additional 1 HD for Small creatures like cats or dogs, 2 HD for humanoids, or even 3 HD for especially large creatures such as Giants. It takes a number of rounds equal to the HD of the creature’s for the Thing to assimilate their victims. Things gain an additional attack per round for every 3 HD above their original.
Things may split themselves into multiple creatures with as many HD as the original has to contribute, (e.g. a Thing with 4 HD could split into a pair of creatures with 2 HD each, or two creatures with 1 HD and 3 HD, etc.) Each of them is an independent creature and has no inherent loyalty to the Thing that it originated from. Things can communicate with one another by means of an ultrasonic frequency that most creatures cannot hear.
Things can perfectly mimic any creature that it has assimilated, both mentally and physically, though this imitation only extends to organic materials. It cannot replicate things such as a victim’s weapons, armor, tattoos, make-up or objects such as fillings or earrings.
Things are immune to effects such as critical hits, sleep, paralysis, stunning, and anything that modifies their physical forms such as Polymorph spells.
Things may use Stealth as if they had a 5-in-6 in the skill, or as if they possessed an 80% in Hide and Move Silently, as appropriate for the system.
5th Edition Stats