With not quite enough in common with elves to be understood by them, nor enough with humans to not stick out, half-elves often find themselves at odds with both parts of their heritage. There are rare examples of half-elves being the result of a union between elves and other races closely related to humans, but such births are extremely rare, and children between half-elves and any other race they can interbreed with, typically result in a child of the other race.
While half-elves are often treated as one kind of race, significant differences are depending on their elven lineage. For instance, those with a Sand Elf parent will deal with the desert heat better than the child of a Sea Elf, but they in turn are much more adept in water.
Half-elves are much more similar to humans than they are to elves. They mature slightly slower than humans and have slightly longer gestation periods. They are also able to interbreed with many other races the way humans can, but this tends to remove the genetic inheritance of their truly elven side.
Half-elves may or may not have a reborn elf soul the way true elves do. What is certain is that they don't remember previous lives and they need regular sleep rather than meditation to regain their strength.
Half-elves retain some of the adaptability of their human parent, but also the ability to see in the dark and to resist some influence on their mind from their elven parent.