Sydaan Nyx, also known as Amanda Stagwind, Sometimes known as Myst Dune, and many other names, is a very old and very subtle changeling who is the most recent in an old and powerful family dating back to before the calamity. 
She is the wife of Jurgen and in her attempt to find him after he left, lost her memories temporarily, but as time has gone on she has regained them, and more. 
Now she has made deals with great powers, defies the raven queen and is willing to do great good and great evil to keep her family safe from harm.