The main property of everything in Fairyland, haunting beauty, is hard to get across at the game table. I’d prefer to double down on a more visceral property. Everything is too big (or maybe you are too small).
Flowers and mushrooms are six feet across. Bugs are the size of horses. (Giant bees and ants, with their neat orchards and farms and mighty queens, can be major fey political players.) Trees are redwood sized or larger. Cliffs and mountains brush the moon, which hangs huge and bright in the perennial dusk.
Narnian talking animals are one size bigger than usual: little animals like foxes and hedgehogs are halfling sized, deer are rideable, and predators are dire (size Large or larger).
Elves are taller in Fairyland, and taller again in their demesne. Your elf PC might stand a foot taller as soon as she steps through a fairy gate. An elf lord on his throne might be ten feet tall. Nevertheless, the whole fey court might fit on the branch of an massive, ancient tree.
Fomorians, the fey giants, should be a big deal in Fairyland politics. I’d also pepper the clouds liberally with cloud giants.
The only small things are the childlike common folk, from gnomes to sprites.
In a lot of ways, Fairyland is like a memory of what it’s like to be a kid: magic and wonder is heightened, you’re not sure what the rules are, time has no particular meaning, and everything is much bigger than you, especially those in power. And bad things lurk in the darkness.
I love this idea and I will probably use it in the next session of my campaign, when the PCs go to my setting’s version of Faerie.
Be careful when going through with this idea. Your Players are going to get used to a world like this quickly, diminishing the fear factor. Making everything bigger is an idea that tends to be overused in order to give the Players a sense of foreboding, fear, or wonder…but mostly fear. Making an entire campaign like this will certainly inspire great feats but eventually all that previous fear is going to dissipate. Maintaining a constant sense of fear and dread is extremely difficult and some Players may be very opposed to this idea. This tends to be why the big baddies get bigger during fights, to signal a challenge. Making an already big villain bigger diminishes this effect.
Scaling things up to the very upper edge of belivability is one of the most effective methods of making a world feel wondrous and magical. Someone who understood that was Tolkien The way he describes ancient things you always get the impression of them being literally larger than life. It doesn’t have to be ridiculously big and at a completely different scale, just bigger than you’d think it could realistically get. If you go too big and make humans feel tiny like mice, then you get a different effect and it feels like Alice in Wonderland or something like that. Putting the slider at 110% means everything still works like normal, but is certainly not natural.