Mecheon
Sacabambaspis
Your Prime Materials generally runs on rules and logic. They have their limitations. Not being the real world is meaningless: They might be fantasy worlds, but they're specifically the equivilent of the standard regular.no I get that but the first two is any good setting worth its salt as they are not the real world.
See, the thing about including any plane into the game is everything needing to be in there for a reason. You shouldn't just throw the Abyss in with no forethought, its gotta mean something. Why are you delving into a pit of chaotic evil specifically? Why is this place more important, compared to other alternatives? Planes should be telling something, hence why they're not the real D&D world.a world of stories would be hell it self because people do not think about what it means, most think stories of youth or legends of older days it simply means any narrative it would look alien in ways we would want to burn as most groups of humans have collective narratives even the evil ones.
The Feywild's a reflection of reality, so its one of the easier to use in this. Its got tons of uses. A mirror to look at reality, an even more magical place to act as a counter to a lower magic baseline reality, a hint at glories long past, a way to travel distances on the laws of stories rather than that of stories. THere's a reason D&D had tons of proto Feywilds, and even mythology itself provides several. They're your Annwns, your Avalons, your Otherworld