Immortal Elves are just that, Elves that are, effectively, immortal. Even from Elven standards.
They spent the Fifth World (What we're living in right now) planning and getting ready for the return of Mana in the Sixth World and are getting ready for The Horrors along side the Great Dragons who slept while the Mana was low.
...
Well, that's the idea. The truth is that each one pretty much has their own idea on how that should be done, and we get into multi-millennial politics that made even Dunkie's head hurt. A lot.
Harlequin is the most infamous Immortal Elf in Shadowrun from the reader's point of view as he was a common poster on Shadowland (First-To-Third Sourcebooks were Shadowland posts, just like Fourth is JackPoint posts.). JackPoint member "Frosty" is his apprentice (And possibly the first Immortal Elf born in the Sixth World.), and is supposed to be taking over for him, but isn't doing that good a job.
From the point of view of John Q. Wageslave, they're not even rumors. From the point of view of Jane Q. Shadowrunner, they're rumours. From the point of view of FastJack, well, he's seen too much weird drek to rule anything out, really.
