I'm currently running a West Marches style hexcrawl in D&D 5e, so I've been thinking of how to make the implied D&D setting more interesting. Anyone who has gamed with me before knows I love a few things in fantasy settings: Trolls, Elementals, and the Fair Folk. I like faeries that are dark and vicious and utterly incomprehensible to humanity. In horror gaming (where all monsters should be a metaphor for something) I treat them like magical sociopaths, doing horrible things with a smile on their face courtesy of their total lack of empathy. This extends beyond fantasy settings into urban fantasy and other modern genres.
Elves in D&D then present an interesting problem. In the English literary tradition, elves and fairies are interchangeable and I like to represent that in my games. I don't want to remove elves as a race because some people may want to play one, and heck, half elves are interesting enough (from a story perspective, ignoring mechanics) to grandfather in the whole elvish race. I'm presented with an issue in that case, how do I include Elves-as-fey when I have to include Elves-as-mortals. When I've tackled this problem before, I created a visually similar but distinct race of fey foot soldiers known to the general as Fey Elves. For my current setting, I'm going to do something slightly different.
“Elves as we know them were born from the faerie realms, even a child could tell you that. They couldn't, however, tell you why. There are two courts of the fey, sometimes called the Sun and the Moon Courts, the Winter and Summer Courts, or the Jade and Mithril Courts, the Fair Folk are capricious and frequently change names after one of their frequent coup d'etat. In the old days, when the homeland was still wild and dark, the fey would organize hunts of the pitiful scared mortals. This phenomenon grew less prevalent over time as we beat back the savage wilderness and tamed it. Eventually, it reached a point where the fey were able to step through to our world, but once there, they couldn't leave. The land wasn't wild enough to create a path back to their strange and savage realm. As the years went on, the Elven huntsmen grew weak and tired, their connection to Faerie draining in their absence. Eventually they became mortal and civilized, becoming the elves we know today.
Not all Elves joined in these hunts, the whims of a Fey creature are ever changing and the time it took for the paths to close was but a short time in the eyes of an immortal creature. Those elves retain their fey nature. The new world is still a wild, untamed place and the fey are easily able to cross over. The two courts are distinctive in culture and abilities.
The Winter Court (also called the Moon and Mithril Court) stick to the dark places of the world. These elves, called Drow by some scholars, are tall and pale skinned. Their hair is pitch black and they frequently wear large cloaks of raven feathers. Their highest art form is torture, exhibitions of their prowess can go on for days, driving kidnapped mortals mad with pain but leaving them alive and broken. The politics of the Winter Court are frequently lethal and advancement is usually secured over the body of a Drow's superiors. Clerics and Green Knights of their Archfey patrons are common and use their powers to prolong the suffering of their captors. They are a quiet and solemn culture, eschewing the ostentatious and rowdy displays of their Summer Court fellows.
The Summer Court (also called the Sun and Jade Court) is often mistaken for the Winter Court's good counterpart. This is sadly untrue as this court contains just as many vicious killers as the Drow. These elves are often called Eladrin, by those experts on the fey realm. Their hair and eyes are golden, fiery red, or somewhere in between. They dress in colourful tunics and often wear crowns or garlands of flowers. They enjoy combat, be it war or duels and consider it the most important skill for an Eladrin to have. They usually determine their leadership through duels to the death. The victor of these duels is not always the survivor. They judge the victor based on their performance, looking for strong aesthetic in their movements rather than martial prowess. This means that on rare occasions, the Summer Court will be lead by the dead body ushering in the reign of a Headless King or Queen. They don't reanimate these bodies, but instead have a bloody period of conflict with many Eladrin competing for regency.“