On page 126 in Guardians of the forest there is an adventure seed talking about the court of dark summer. I just have the RoP:Faerie but skimming through I didn't see any section on courts. Has anyone expanded on this adventure seed? Where in the RoP can I find some info on the dark summer court?
There are no specifics on 'dark summer' in RoP:F, but a lot about Courtly Faeries (p.80ff) and Divisions of Time (p.84ff), which should give you ideas.
What One Shot said.
Also, just take your cue from the words "dark" and "summer". IIRC there is a slight description in the GotF text about these. But to me "Dark" sounds like they are active at night, malign or at least annoying to humans, and have skin and clothes in dark colours. "Summer" sounds like they are strongest during the summer, have powers of warmth. And they are bound to dislike sunlight and the cold.
So, give them a power to light a bonfire of black flames which spread darkness even during the day. And have trees blocking this darkness cast a "shade" of daylight...Heck, that sounds so cool I might even use that myself in the RHina saga I'm playing in.
As for "court" I think this may be a remnant from earlier editions. Sonce GotF was published way before ROP: Faeries the two books may not agree completely. Pre 5th ed I think faeries were most often organized in courts to simulate human behavior (although only as a nobleman's court). With 5th ed RoP:Faeries this has become somewhat less universal, and although still one type opr theme of faeries 5th ed is more clear about what faeries want and what they do. Although I take thay book very lightly in use since faeries are not a primary focus of my sagas merely a backdrop.
GotF mentions Faerie courts a lot, just look at the "court of the four seasons" in the first part of the book. But having faeries portrayed as a court is also a quite easy method IMHO.
GotF mentions dark, fire, warmth and agriculture as defining the Court of Dark Summer.
I'm no expert on the area in question. With that caveat in mind, I might consider trying to incorporate suggestions of ominous storm clouds(dark), lightning strikes(fire causing), oppressive humidity(warmth), etc. - those elements of summer that can be less than enjoyable to humans (and their agriculture). Of course, the past day here where I live has been somewhat reflective of that with 30C+ temps, high humidity and sudden thunderstorms with driving rain (no hail though), so I may be a little biased.