Creating a homebrew master villain?

[Varon]

Hey, everyone!

So I'm working on creating a Celtic legends/Arthur mythos/alternate world campaign with plenty of the Fae involvement, and I realized that I probably need to flesh out the main villain a lot more. Unfortunately, since I'm thinking the villain will be a very powerful Fae who, while once good, has gone bad in order to reunite the Fey world and the mortal world, I've been trying to find some more Fae stuff for villain ideas, especially some sort of Fae king. I can't find any anywhere or even where to really start. You all have any suggestions on how to go about creating this villain?

[GalacticAxekick]

I'd base the villain on the Mage (https://www.aidedd.org/dnd/monstres.php?vo=mage), Archmage (https://www.aidedd.org/dnd/monstres.php?vo=archmage) or Lich (https://www.aidedd.org/dnd/monstres.php?vo=lich) stat blocks depending on the intended power level. Spells could be replaced with the Warlock's Archfey patron spells, plus anything thematically similar.

Borrowing features from the Elf and Gnome races, or the various Fey creatures would also be appropriate. Charisma-based spellcasting, darkvision, maybe amphibiousness, mimicry, speak with beasts & plants. Druid spells/features might be appropriate, if you want to play up the relationship with nature.

After that, it's all fluff. I like to use backgrounds for my NPCs to help flesh them out, but you can decide the villain's personality, ideals, bonds, flaws, history and skills on your own too.