Well, at the risk of sounding cliche in this world building A-Z challenge, 'E' is for Elves!
The Elven race has always intrigued me. Even though I never read Tolkien's books until much, much later in life, his perception of the race is exactly how I imagined them.
Of course, I have my differences to the race. Every fantasy author will see them differently. But for world building purposes, let's take a look at some of the differences in the fantasy genre.
ElfQuest: Wendy and Richard Pini portrayed Elves as being smaller than humans, almost the size of a child. They didn't start off that way. The "High Ones" were not just the very first Elves, they were significantly taller in stature. They had a thumb and three fingers, they could speak telepathically, (called "sending") and if and when they discovered their true Life Mate, the term for discovering them was "Recognized". Each would Recognize the other's soul or "true self". Their existence was explained as a "spaceship" crash.
Tolkien: The Elves in Tolkien's "Lord of the Rings" and "The Hobbit" are magical beings. Fair haired, graceful beings. Some with dark hair. They didn't vary much in color or stature. They looked like any other human being with pointy ears being the only exception to their appearance. They did not feel cold or intoxication. They were light of foot, as displayed by Legolas' walking on top of snow or lightly leaping from the ship in "Return of the King".
Other depictions of Elves explain them as being as tall as humans and hair and eye color can be just about any color imagined. World of Warcraft shows Elves with long, pointed ears that flop when they run. I don't like many of those Elves. But their skin color is different, whether it is a Night Elf with glowing eyes or a Blood Elf with an arrogant attitude.
Personally, my Elves are as tall as humans, have just the right amount of point to their ears to indicate their race. They can't get drunk unless they consume at least ten times as much as a normal human and they don't age. They can be killed, of course. Any life can be taken. However, if an Elf lives to a ripe old age of a thousand years and has decided enough is enough, they can choose to leave their current existence and allow their energies to return to the earth.
How do you imagine Elves? What makes yours different from what people consider "The Norm"?