Yeah, I think, for what you're asking, the bases have all been covered. As the BBEG scheming the big schemes, the truly powerful masterminds, are numerous but across fairly few creature types.
- Dragons. Obviously.
- Devils, moreso I think than Demons [other than your Grazzts and Lolths]. But Demons, too, particularly those in the upper tiers of power who are looking to get ahead/spitting distance of becoming "lords" in their own right [like Type 5's & 6's].
- Cambions & Half-Dragons, falling in the Demons or Dragons categories, respectively.
- Rakshasa and Oni are basically two sides of the same coin, schemers by design, fulfilling the same space as Devils. But their dreams are usually of temporal power, tending to plateau at "worldly comforts" levels, moreso than "dominate the world/enslave the mortal plane."
- Barghest, I've used also, falls into the "ambitious Demon" or Rhakshasa/Oni camp...but can certainly be played with the preternatural capacity for masterminding big things.
- The Undead Lords: Liches, Death Knights & [Ancient/Progentior] Vampire Lords. Immortal, immensely powerful compared to 99% of [NPC]mortals, and almost always after some ultimate -as yet not achieved or achieved-lost-sought again- goal.
- The Aberrants: Mindflayers, Aboleths, Beholders have the intelligence, power and alien/inscrutable goals.
- The Drow. Despite the caveat to not include humanoids, they are basically an entire race of/default D&D culture/flavor as despicable schemers...and they are the only "PC-permitted" race
also listed in the MM
[ok, not counting half-orcs, but they don't have the smarts to be what I would call "masterminds" anyway. Very capable as villains, even leaders/generals/etc... but not masterminds.
- In keeping/lumping in with the Drow, I would be inclined to add "Dark/Unseelie" Archfey to the list.
There are plenty of other evil creatures with intelligence. But the capacity for weaving webs of plots within plots, pulling strings and maintaining unquestioning control and power throughout it all...I think that list covers your vast majority.
Sure, Hags can scheme. Succubi can scheme. Things like Duergar, Derro, uniquely cunning/capable Orc/Hobgoblin warlords, particularly intelligent Giants, Efreet, Charismatic Cultists and hyper-Intelligent Wicked Wizards...all of them can plot, sometimes even elaborate, schemes...kinda necessary to qualify as "Potentially Recurring Villain 101."
But mastermind? Not necessarily imho.
