Dark Elves

Dark Elves are one of the standard Elf varieties. They are a staple of standard fantasy found almost always in those that feature elves. In those where elves are portrayed as their nauseatingly good archetype, dark elves are usually typecast as the polar opposite, usually as chaotic stupid edgelords who get off on traditional evil, sadism and looking really sexy doing it. While a hawt elf maiden might be chaste, a hot dark elf priestess may theoretically promise you access to her silky ebon be-thonged areas should you prove yourself worthy, only to tear off your wang and use it as a musical instrument to summon spider demons against her enemies (i.e. everyone).

They tend to have most (if not all) of the following characteristics:

• Dark-grey skin and white hair.
• Overtly supremacist ideology ("You are but beasts of burden that can use tools that we shall use as we wish, disobey our dominant will and face agony that, if you are lucky you will quickly die from", most regular elves generally don't go beyond "You short lived members of younger races are foolish, short sighted and lack grace and perspective, go along living in squalor as is your way well away from us if you must but leave the important decisions to us if you know what's best for you"), even more so than their homosexual bretheren.
• An economic system based on slavery.
• A system of promotion based on might-makes-right (i.e. killing one's superiors to take their position). This is distinguished by the stereotypical kraterocracy of fantasy "bad guy races" by being a lot more Machiavellian and scheming and making it obvious is not usually considered a good career move, or even considered vulgar.
• A culture of eugenics where only the strong survive and only the strongest get to breed, which usually ends up just making them weaker rather than stronger for some reason.
• A fondness for spikes in everything, from fashion to architecture.
• Underground dwellings. The colder, darker, shittier and edgier the better.
• A backstory where they have rebelled against the other elves, lost some war, and been exiled to the above. Naturally they are somewhat miffed about this, and really hate elves. Even more than dwarves, which is saying something.
• Being slaves to some evil god or demonic entity whom they worship but hate, but usually being too proud to admit their enslavement to themselves. Rebelling against said entity or its plans for them will usually be strongly implied result in their race being destroyed, i.e. by all killing each other or having their souls sucked out. The priesthood is generally, but not always, matriarchal.
• A BDSM theme. It can vary in setting from self-mutilation like Hellraiser cenobites to just wearing black leather and bodices a lot.
• An inference that if they ever got their shit together they'd be a huge threat to everyone in the setting, but they they're always too busy backstabbing each other to ever do that. Hmm who else is like that?
• Skills at sneaking about, backstabbing, and poisoning.
• Obsession with arachnids (spiders almost always, some of the time it’s scorpions), often taking aspects of their culture and nature directly from arachnid lifestyle: deadly competition with siblings, killing mates after the act, poison, disabling enemies (especially to paralyse them and victimise them while helpless), and so on. They also like bread with spiders in it, because that's a thing.

Dungeons and Dragons

In the various Dungeons and Dragons games (and their spin-offs, like Pathfinder), Dark Elves are usually known as Drow.

Warhammer Fantasy

Kitbashing Warham Goblins and Warham Dark Elves can produce superior results.

In the long past of the Warhammer Fantasy world, the Dark Elves were once just elves. Then, heir-apparent Malekith found himself passed over when it came time to choose the Phoenix King, and he started a civil war. When he lost got bored, he and his followers (called the druchii in their language) were exiled left across the ocean.

Presently, the Dark Elves inhabit and dominate Naggaroth, the Warhammer World's analogue to North America; this might tell you something on how GW views the Colonies. Their population is concentrated in six major cities, including the capital city of Naggarond, but they also inhabit massive city-ships known as Black Arks, kept afloat by the magic of the Witch-King. Where the arks go reaving, things burn, slaves are taken, and fat lewt is piled high and sent back to Tortureonto (Karond Kar) or Evil Fredericton (Har Ganeth) or Hellifax (Clar Karond) or whatever. Don't mess with the corsairs. Unless you're a Norscan or a Hung, in which case, shine on you crazy Chaos Viking/Hun!

Then we have the shades, a bunch of hosers that live in the wilderness full of beasts that Chaos dragons think twice before messing with.

The Dark Elves are also the biggest jerks in the universe- The War of the Beard? Oh, we raided the dwarven caravans that started it all! *Mad cackle* JUST AS PLANNED!.

Coincidentally, this also leads up to Nagash's rise to power with his Necromancy since the trio of dark elves that were ordered to start the war ended up in Khemri, warhammer Africa, where they were shipwrecked when trying to escape. They were later found and captured by Khemri guards, then tortured by Nagash for information about magic and other high quality stuff to become powerful and evil. So yeah, Vampire Counts nor Tomb Kings would never exist if it weren't for the Dark Elves and The End Times would never happened. Not as planned for the Dark Elves.

Males are forbidden to use magic since Malekith's mum Morathi said that he would one day be killed by one. Not like anyone cares, but it's probably a plot by her to take the throne.

Among their traits are that their nobles ride exothermic carnivorous reptiles into battle. This is weird since their homeland is quite chilly, so you would think that they would be sluggish and inefficient mounts (hence why they have the rule 'Stupidity').

Warhammer 40,000

In Games Workshop's quest to give every WHFB race a counterpart in the grim, dark future of Warhammer 40,000, they created the Dark Eldar -- all the hedonistic fun of the Dark Elves, but in space!

Other

While D&D's drow have pretty set the dark elf mould as cruel, dark skinned and spidery, they were not the first nor is this obligatory for anything that might be called a dark elf in fantasy. True, most franchises which have dark elves are vidya and can be ignored, but there still are some worthy of mention:

• "Dark elves" (Moriquendi) were mentioned in Tolkien's works, but they weren't (necessarily) evil, simply elves who hadn't seen the light of the two trees in Valinor - which was actually most of them. In the Silmarillion, Eöl was known as "the dark elf", perhaps for his thing for living in dark forests and wearing jet black armour. Some elvish characters did certainly evil deeds, most famously Fëanor and his sons, three kinslayings and trying to abduct Lúthien. Fëanor's kin were of Calaquendi, so they don't even were Dark elves technically, only by their deeds.

• And from the Norse myths from which Tolkien borrowed from heavily, the dökkálfar were dark elves who resided in the underground world of Svartálfheim. Norse myth often identified them as dwarves, either accidentally or intentionally, and so you can take most of the dorfy attributes from them such as being good at forging and greedy little shits. (One might assume later fantasies wanted those attributes combined with more sexy.) You'd probably know all about this if you were into comics, as Marvel's Thor universe mention them a lot. As for svartálfar, whose name is partially derived from the rootword for "swarthy" (meaning "dark-skinned")... well, let's just say Nordic mythology can be a real tangle of worms.

• In The Elder Scrolls vidya, dark elves (Dunmer) were originally just golden-skinned elves (Mer) but became ashen-skinned and red-eyed as a curse from Azura for rejecting the gods (Aedra/Daedra) and ascending some of themselves to godhood using a divine heart they found to worship instead. Yeah, TES is pretty off the wall like that. In a bit of a twist, while many (most) of the elves in TES are genocidal assholes, the Dunmer are not, but they still have that overwhelming self-superiority complex every other elf of any variety has. You filthy N'wah!

• While never called dark elves, the Seelie of the Plane of Fairie a.k.a. the Feywild are D&D's version of pre-Tolkien not-nice elves of traditional myths: chaotic, unpredictable, (literally fay!) elf-like beings of great power that care little for mortals: not evil, but certainly not good. Unseelie are their genuinely evil counterparts. While the Seelie may leave you to starve/age to death because they imprison you as a short diversionary mortal sexual plaything then get bored and forget about you, the Unseelie will be happy to invite you for dinner... as the first course. The truly horrifying thing about the Unseelie however is that if you google that word for any decent pictures for the gallery, you'll find only Twilight or Drizzt-tier romantic fanfiction. Remember: dark elves like it when you scream.

• In Shadowrun, dark elves are some weird subrace of metahuman elves that can't tolerate light and camouflage themselves with a very fine coating of fur on their skins. I wish I was kidding.

• In Fighting Fantasy, the forgotten grandpappy of Warhammer, dark elf backstory and description closely follows what the dark elves in Warhammer were to become, just with a lot less writefaggotry to flesh it out over the decades. Yeah, Warhammer took a lot from that old fluff. The original concept was still nicked from D&D though.
• Warhammer's portayal of dark elves is in part inspired by the Elric of Melniboné universe by Michael Moorcock, the evil, pallid elf concept and the eight winds of Chaos were adopted from there. Elric (or Malus Darkblade as we know him) is the last of the Melnibonéans (Druchii). Centuries before Elric's birth, Melniboné ruled its world through sorcerous might and sheer power. However, by the time of Elric's birth, it has slipped from its preeminent place, being one of many nations. Its people, the Melnibonéans, are not wholly human, resembling instead the elves of legend — skilled with magic and beautiful, though psychologically similar to cats, with a callous nature. They are bound by many ancient customs. Darkblade, or the Warpsword of Khaine, is basically GW's take on Stormbringer. The Daemon ('Tz'arkan') is actually in the sword in the original tale. Michael Moorcock's intention was the turn the idea of the traditional high fantasy elf on its head. GW ran with the idea.