I've been working on converting all 300+ monsters from the BECMI and Mystara settings to 5th edition, in the hopes to publish them as a game book. Seven chapters, each with a different narrator. After finishing the chapter on fey, it came out rather light on creatures. I grabbed some from folklore to give the section a bit more meat. So from Scottish lore, the forwyn oedran. A fey that manipulated time, stealing years from those she thought living a wasteful life and gave it someone she thought more worthy. Gamewise she's all about time manipulation. Can't actually damage people, but can age them with a touch. Also can haste or slow at will, and even stop time if pressed.