Not positive whether this is the sort of question you answer, but what’s the best way (if you know of one) to make an NPC of given race more powerful than others if it’s not listed in the books? IE. The leader of a group of sprites, etc.
I can answer pretty much any question you want! I’m not super active on this blog right now, so it just may take me awhile to answer (like this one!)
I personally think the best way to make a more powerful version of an NPC or monster is to give them class levels. Even just one or two levels of a class makes a big difference in what an enemy can and can’t do, but without changing their power level drastically. I’d say every two levels of a class boosts an NPCs CR by 1. Class levels are also great for differentiating an enemy situationally. Fort instance, if you have a leader for a group of sprites and you want those sprites to be involved in a plot where they’re stealing from forest travelers, you might give their leader some Rogue levels, to show they’re skilled in thievery.
Another way, and my preferred way if you’re just making one enemy the leader of several others, is to give them legendary actions. Legendary Actions are 5e’s perfect solution to creating boss monsters. It gives them extra actions without breaking action economy entirely, allows them to do cool things they might not otherwise, and puts them at an obvious advantage over both your players and other enemies. Legendary Actions are honestly one of my favorite things about 5th Edition.