Doppelganger

@ doppelganger
Difficulty	11
Attacks	Weapon 1d12

@ doppelganger
Difficulty	11
Attacks	Weapon 1d12
Base level	9
Base experience	191
Speed	12
Base AC	5
Base MR	20
Alignment	0 (neutral)
Frequency (by normal means)	1 (Very rare)
Genocidable	Yes
Weight	1450
Nutritional value	400
Size	Human
Resistances	Sleep
Resistances conveyed	Causes polymorph
A doppelganger: has a head, a couple of arms, and a torso. is omnivorous. is not a valid polymorphable form. is a human. is normally generated hostile. is strong. can pick up weapons and food. can be seen through infravision.
Reference	monst.c#line2173

For the player race in SLASH'EM, see Doppelganger (starting race).

The doppelganger is a shapeshifter that appears in NetHack.

They will imitate player monsters and occasionally monsters that may be created by summon nasties. Each turn they have a one-sixth chance of attempting to change form; one-seventh of these attempts will turn them into a nasty and two-thirds of the rest will change them into a random player monster.

Doppelgangers that are imitating player monsters will take the rank titles for that role, based upon its level - a doppelganger imitating a fourth-tier Healer appears as a "Dresser", while one imitating an equivalent Wizard appears as a "Magician".

Strategy

Doppelgangers are considered human for sacrifice and cannibalism purposes. Eating a doppelganger corpse will cause you to polymorph, unless you have unchanging. This will polymorph pets as well, which is one of the dangers of leaving carnivorous pets (especially purple worms) near doppelgangers.

The following information pertains to an upcoming version (3.7.0). If this version is now released, please verify that it is still accurate, then update the page to incorporate this information.

Pets will no longer eat shapeshifter corpses unless they are starving or on the verge of untaming.

Variants

SLASH'EM

In SLASH'EM, doppelgangers are a playable race, with high stats, natural protection, and, as one might expect, the ability to polymorph at will, via the "#youpoly" extended command. However, doing that will cost power. A very useful tactic is to polymorph into something when going near a hard battle, to have both the benefits of the new form, and those of reforming as a doppelganger when you should die.

An excellent choice of Role for a doppelganger is a monk, since these would benefit from the polymorph much more than anything else.

Origin

"Doppelgänger" is a German word that literally means "double-walker", and refers to a biologically unrelated look-alike or double of a living person. In fiction and mythology, they are often portrayed as ghostly or paranormal phenomenons, and are usually seen as harbingers of bad luck; other traditions and stories equate a doppelgänger with an evil twin.

Encyclopedia entry

"Then we can only give thanks that this is Antarctica, where there is not one, single, solitary, living thing for it to imitate, except these animals in camp."
 
"Us," Blair giggled. "It can imitate us. Dogs can't make four hundred miles to the sea; there's no food. There aren't any skua gulls to imitate at this season. There aren't any penguins this far inland. There's nothing that can reach the sea from this point - except us. We've got brains. We can do it. Don't you see - it's got to imitate us - it's got to be one of us - that's the only way it can fly an airplane - fly a plane for two hours, and rule - be - all Earth's inhabitants. A world for the taking - if it imitates us!

[ Who Goes There?, by John W. Campbell ]

Xander: Let go! I have to kill the demon bot!
Xander Double (grabbing the gun): Anya, get out of the way.
Buffy: Xander!
Xander Double: That's all right, Buffy. I have him.
Xander: No, Buffy, I'm me. Help me!
Anya: My gun, he's got my gun.
Riley: You own a gun?
Buffy: Xander, gun holding Xander, give it to me.
Anya: Buffy, which one's real?
Xander: I am.
Xander Double: No, _I_ am.

[ Buffy the Vampire Slayer, Episode 5.03, "The Replacement" ]