Ultimate Bestiary: Secrets of the Fey

From publisher blurb:

The Fey Beckon

In the twilight of the trees, between uncounted standing stones, at the meeting of worlds where time grows strange, they sing their songs, and wait...

Ultimate Bestiary: Secrets of the Fey presents a variety of the classic fey and fairy tale creatures, including centaurs, fairies, merfolk, hags and nymphs, fleshing out their cultures, habits and habitats, and introducing a wealth of stat blocks to challenge your players from level one to the end of their adventuring careers.

So pass the threshold if you will, but make no deal, accept no gift and, above all, trust no fey.