I've never been a fan of elves in games. Or in fiction for that matter. They usually are presented as humans-but-better, including aping human civilization (but in tree houses!) and being biologically similar enough to humans to interbreed and create half-elves which are even more of the humans-but-better. Why play a human when you can play an elf or half-elf? Why aren't there half-dwarves? Why would an elf mate with a human? That last question leads to uncomfortable conclusions along the lines of half-orcs.
No sir, I don't like it.
But because I'm trying for once to make a somewhat traditional DnD experience for my players, I'm including elves in the upcoming Maze of the Blue Medusa sessions. Albeit with my own spin on them.
Same stuff as in the Player's Guide, mechanically speaking.
Elves speak faerie. Don't remember if it says that in the book or not. There isn't an "elvish" language.
They can choose any class available to humans, but need 25% more experience points to reach the next level.
Elves are human bodies, kidnapped just after birth, and inhabited by a faerie spirit. This spirit changes the body on a genetic level into an elf. Faeries do this in order to experience the world as humans do. But since they aren't human, they get some things wrong. Give them a break, they're tourists.
As children, elves are very mischievous and quite like their faerie kin in behavior. As they age and contact with other species increases, they mature. Older elves who have lived among other species for long periods of time forget their origins and consider themselves to be a unique species unto themselves. These ancient elves live in human society, usually as landed gentry, aristocrats, and powers-behind-the-throne. They generally look down their noses at commoners, and will not deign to speak to young elves.
Elves have natural abilities that are similar to their original form, with the exception of flight. A sprite form will have sprite-like powers, a pixie form will have pixie-like powers, a leprechaun will have leprechaun-like powers (and an affinity for gold).
All that being said, elves and faerie-folk live and play together and instinctively get along.
Other than ancient elves who've forgotten who they are, the following is generally true of elves:
Elves do not live in cities. Elves do not pray to gods. Elves do not forge steel or plant crops. Elves do not build houses or castles. Elves do not practice civilization as humans know it. They prefer the night time under the moon and stars.They may or may not wear clothing; depends on the situation or weather.