Fey of the Elder Starlight

Last time in my series on the fey, I looked at goblin markets and ways that DMs can present them in-game. This time, I’m going to an upper end of the fey power-scale. The goal of this series from the beginning was to populate some of the Challenge Ratings that don’t feature fey. How about CR 30, and the kinds of fey that might make the Archfey nervous?