Gonna go obscure on this one. The Wood from Uprooted. Without going into spoilers, it’s a forest that wants to expand and wipe out all of humanity. It is capable of fairly strong fey coded magic focused on corruption and mental manipulation.
If you go on a walk through The Wood and don’t die, you need to immediately have your body magically purged because if you don’t then the tiny whiff of corruption that you inhaled will grow inside you like a parasite and turn you into a weapon that it will use against your family. Worse, you absolutely will not think to do this without someone else pointing it out because a few hours in the wood is enough that you’re already compromised, and if you were dumb enough to eat anything you need to be put down immediately. Animals are not immune to this, either, and once they are corrupted they can pass that corruption on to others.
This is all bad enough, but even worse is the part that makes it count as a villain. It is not a passive or animalistic entity. It is intelligent enough to manipulate politics, do infiltration with its puppets, create cursed magical items to spread its corruption, etc.
More importantly, it’s patient. It’s difficult for an extremely powerful wizard to contain it, even when it’s half assing its attacks… and it will half ass its attacks for decades at a time because it knows that the stupid humans will forget about it and stop taking it seriously.
So it builds up its defenses, makes sure that no one could possibly intrude on its territory, and attempts dozens of low effort attacks a year. Then one of them will inevitably slip through, cause some chaos, and that’s when it will eat an entire peasant village while the nobles and soldiers and mages are distracted.
If it weren’t a YA novel antagonist vulnerable to impetuous teenage girls with special powers in the midst of discovering who they really are, it would probably completely envelop a continent. We do know it’s repelled by salt, so people on other continents and islands would be fine then. For a while. Until it can figure out how to plant just one seed that manages to bear fruit.
Possibly the best comic-book villainess of all time.
