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).

Well, one of Tolkien's more important stories has as a main character the daughter of a Maia and an Elf- The Lay of Luthien, in all its incarnations. You could use Luthien (the daughter) as a reference (the story is in the Silmarillion). Luthien was apparently capable of shape-shifting (herself and others) and magic beyond that of most elves, though part of that could be because it was the First Age.

I would probably make the Second Age offspring of a Maia and a Numenorian less powerful, since Numenorians have only a little elven blood. Also, this NPC could have different powers than Luthien, to make it more in line with being the child of Sauron, rather than just your run of the mill Maia.

Some possible powers? It would probably be mostly sorcery spells as magical abilities, such as: Command, Evoke Fear, and Shadow of Fear. You could throw in some others, as well, but I would keep the total down to about three, personally. Another route that you could go would be to just make up new racial abilities for it and put in whatever you like.