Maia/Numenorian offspring?
Currently re-watching the movies, and that got me thinking about my old chronicle idea that I still haven't used.
One of the important NPC would be the offspring of Sauron and a Numenorian princess. It is through her he manage to free himself from their prison, get to the kings ear, and get them to launch the attack against the undying lands.
If I recall correctly, the royal house of Numenor can trace their lineage back to Elronds brother. So they have part elven blood in them.
So... anyone who wants to chime in with ideas of what kind of powers an offspring like that should, or should not, have? :) The only need to haves are "passing of as human" and "immortality" (as in not aging).