Lost Lineage Volume I: Phantom Elves

From Introduction:

This installment of Lost Lineages focuses on the Lythain, commonly referred to as phantom elves. The Lythain are significantly different from the common elves presented in the core rules, but great effort has gone into making sure that they can exist in the carefully woven fabric of your campaign without the GM having to put in undue effort or use a shoehorn. That effort notwithstanding, if phantom elves do not fit into your campaign per se, you can still use the items and classes presented in this product to give a bit more depth to your own elven cultures.