Quote from wordflyerjosh >>

Quote from DrWylieAlexios >>

I like the notion that they are guided by their true neutral alignment. As an example, in the Lost Mine of Phandelver beginner box adventure, they are working for the drow, posing as drow. Yet, when given the opportunity to acquire the map to said mine and captivity of the dwarven owner, they would destroy the map and kill dwarf, preferring to keep knowledge of the mine kept from both sides: the evil drow and the good dwarves/PCs.

 The Doppelganger wants to destroy the map because he wants to prevent the party from re-acquiring it, not because he doesn't want either side to get it. Make no mistake--he works for the black spider, but the black spider doesn't need the map, because he is already in the cave. 

Yeah, the "will switch sides to keep the balance" interpretation of the neutral alignment hasn't been applied since before 3rd edition. Neutral means the doppelganger simply ignores moral questions in pursuing its goals. There's no malice, so it's not evil - just doing what doppelgangers do.

Quote from SethTheFrank >>

Ok, but what do they actually want? Just money and ease? 

 I'm pretty sure they're after the weed.  Have you ever known a doppleganger who doesn't?

I think this one is indeed sorely underdeveloped. It´s an amazing tool for the DM to create spy plots and be a continuous annoyance to the players. It can be anyone and it senses motives, thus can respond appropriately and elude detection. In my campaign I have one that started as a goblin chiefs pet, but survived the encounter and keeps stirring up trouble by steering various evil factions towards their home base town. Now and then they sense that there´s more to the happenings, yet they cannot capture the full picture. It shouldn´t be overused as if it where behind every plot it´d be a Bolas-syndrome, but as a running foil I really find it a useful tool.

Honestly, most monsters in D&D don't have any kind of racial goal. Even individually, many don't have one because it's assumed the PCS will stop them anyway. So it's really up to the DM to fill in that blank.

The best suggestion I've heard for a "racial goal" for the Doppelgangers is basically to have fun. They like to test their abilities with increasingly difficult alter egos. They like to study and manipulate humanoid relationships and social structures just to see if they can. Once they've toppled the kingdom or reunited the feuding families, they disappear and look for a new challenge.

The other suggestions I've heard require them to be Chaotic and/or Evil. They simply like to spread confusion and/or misery by deceiving and manipulating people and destroying bonds and relationships. It's just their nature.

If you want more angsty Doppelgangers, I'd suggest the motive that they desperately WANT to be part of other humanoid societies, but ultimately either get found out or their inherent manipulativeness makes them socially and emotionally toxic and dissolves the relationships around them.

Though, obviously, individual Doppelgangers may have any number of personal motives, as they are sapient

My PC harvested the skin off of one of these (shes a homebrew blood sorceress who is not afraid of harvesting anything off of anyone 😅) she took skin from back, biceps, thighs and calfs. Also she drained blood from it into little bottles she keeps on her.

Would there be any use for the skin or blood of the creature?? I havent found anything online yet so I'm not sure what I can do with it. 

Thank ya in advance!!

Quote from Scactha >>

I think this one is indeed sorely underdeveloped. It´s an amazing tool for the DM to create spy plots and be a continuous annoyance to the players. It can be anyone and it senses motives, thus can respond appropriately and elude detection. In my campaign I have one that started as a goblin chiefs pet, but survived the encounter and keeps stirring up trouble by steering various evil factions towards their home base town. Now and then they sense that there´s more to the happenings, yet they cannot capture the full picture. It shouldn´t be overused as if it where behind every plot it´d be a Bolas-syndrome, but as a running foil I really find it a useful tool.

That is a neat recurring villain.  Doppelgängers are excellent “side” antagonists; slipping around in the background while the PCs are busy saving the world and all that.

Quote from QuxxnMaddie >>

My PC harvested the skin off of one of these (shes a homebrew blood sorceress who is not afraid of harvesting anything off of anyone 😅) she took skin from back, biceps, thighs and calfs. Also she drained blood from it into little bottles she keeps on her.

Would there be any use for the skin or blood of the creature?? I havent found anything online yet so I'm not sure what I can do with it. 

Thank ya in advance!!

 Well, a player could always sell the stuff.  A wizard or Warlock would likely pay 100 or 150 gold for the lot.  A necromancer, transmuter, or certain types of cultist would pay double.

For magical uses, the blood could easily be brewed into a Potion of Alter self that lasts 1d4 hours (much like a Potion of Growth), by anyone who can use an alchemy kit.

The skin could be used to make Glamoured Studded Leather or a Cloak of Elvenkind as though they were a step less valuable.

Doppelganger motives could be pretty much anything, like a normal human's.

 Does the polymorph affect items/clothes, as in a naked doppelganger can transform into a creature that had seen with that creature's apparent equipment or do they need to get appropriate gear first?

Quote from Limrasson >>

 Does the polymorph affect items/clothes, as in a naked doppelganger can transform into a creature that had seen with that creature's apparent equipment or do they need to get appropriate gear first?

 It would have to get the gear, as in knocking them out or killing them, then taking their clothing and gear.

Quote from Limrasson >>

 Does the polymorph affect items/clothes, as in a naked doppelganger can transform into a creature that had seen with that creature's apparent equipment or do they need to get appropriate gear first?

 A mature Doppleganger could likely imitate a target’s clothing, depending on how elaborate the outfit is, but little beyond aesthetics would carry over.

That being said, they do gain greater control over their form with age and experience, and exceptional individuals do exist, so a “greater” Doppleganger that can imitate weapons and other equipment would not be unprecedented.  The psychic abilities linked to its shapechanging would also be greatly improved.

Quote from Limrasson >>

 Does the polymorph affect items/clothes, as in a naked doppelganger can transform into a creature that had seen with that creature's apparent equipment or do they need to get appropriate gear first?

 According to the Forgotten Realms wiki here, they could duplicate clothing and weapons of a studied victim.

"After they chose their victim they duplicated the victim's form, clothing, and equipment, and attempted to kill the original."

The only thing the 5e entry says above is that "Any equipment it is wearing or carrying isn't transformed."  That all being said, it's up to your DM, but I've ruled at our table that they can duplicate clothing and minor things like jewelry and such that lies close to the skin.

Edited to add:  The 2nd edition Monstrous Manual states the following:

"The doppelganger is able to use ESP and can imitate its victim with 90% accuracy, even duplicating the victim’s clothing and equipment."

Quote from ChrisAu >>

Quote from Werdna >>

Quote from SethTheFrank >>

Ok, but what do they actually want? Just money and ease? Ok, as I write this, that sounds pretty awesome. But it seems like they could get that. And then what?

 I agree seems kind of hollow, almost like once they have that they just rest on their laurels.

 They way I have been thinking of them is that they want to be part of humanoid society, but they know that most humanoids are at least suspicious of them, if not entirely horrified.

 sounds about right they want to learn about this worlds customs

has anyone thought of the possiblity of a vampire doppleganger as a bbeg kinda like the gnoll vampire in rotfm meaning that it has unique traits and unique weaknesses

Quote from C4mSH4FT >>

Quote from Limrasson >>

 Does the polymorph affect items/clothes, as in a naked doppelganger can transform into a creature that had seen with that creature's apparent equipment or do they need to get appropriate gear first?

 According to the Forgotten Realms wiki here, they could duplicate clothing and weapons of a studied victim.

"After they chose their victim they duplicated the victim's form, clothing, and equipment, and attempted to kill the original."

The only thing the 5e entry says above is that "Any equipment it is wearing or carrying isn't transformed."  That all being said, it's up to your DM, but I've ruled at our table that they can duplicate clothing and minor things like jewelry and such that lies close to the skin.

 

Edited to add:  The 2nd edition Monstrous Manual states the following:

"The doppelganger is able to use ESP and can imitate its victim with 90% accuracy, even duplicating the victim’s clothing and equipment."

 Unfortunately anything copied this way is still only flesh and blood and cannot be handed of to others, though a group could make it look like they are handing something between them. This is why they prefer to either capture the victim so they can strip them down or slay the victim so they can remove any items that they need to pull off the disguise, though a good doppleganger may actually steal some washing to start and actually find the easiest honest way to make money later possibly dropping a small amount at the houses where they stole the clothes from,

I once had one of my players actually turn out to be one of these throughout the whole campaign, revealing only at the end.

Massive plot twist of insanity. They never trusted each other again.

In the first Witcher book, there's a doppelganger; an excellent story too. It took the place of a rogueish type character and actually did a better job at negotiating and wheeling & dealing than the person it copied. If it would have been discovered by the kingdom, it would have been executed immediately. One of the other respondents here mentioned "being part of society" which is how I saw it in the book. It just wanted to belong.

Never underestimate how much money a doppelgänger spends on illicit activities. it will soon need to re-up.

their entry in the monster manual makes it sound like they could rest on their laurels, but then they don't. They kidnap and impersonate someone rich and powerful, live lavishly until the money dries up from their ludicrous spending, and then move on to kidnap and impersonate someone else rich. Or at least, that's their normal pattern.

Can doppelgängers shape shift into a description held in someone’s thoughts? Basing this off basically ‘seeing’ a description of someone while reading their thoughts.

Quote from LordJustice50 >>

Can doppelgängers shape shift into a description held in someone’s thoughts? Basing this off basically ‘seeing’ a description of someone while reading their thoughts.

 For the average Doppleganger, their mind reading isn’t that good.

But, it sounds exactly like the kind of ability that exceptional specimens would develop with time and practice.