Small warning:
This text includes talking about brainwashing, manipulation and other things. If you feel uncomfortable about these topics, it might be better to skip it.
While I have multiple different villains in my scp canon, I do think that Elya and Dieran are the worst of them only. Not only do they cause the most harm to the foundation and other goi like the Serpent's Hand and the GOC, they are also, among all the villains, the most aware that what they are doing is morally wrong and shouldn't be done. These two just think they are superior to most of their victims. Dieran especially has the opinion that other humans (aside from Elya) are below him.
Their skill when it comes to brainwashing and manipulation is by sure the highest I have in the entire Scarlet Void canon. And while Dieran uses his anomaly, Elya does it without one. The worst thing about Elya is, how his manipulation works. It's very hidden, and he takes his sweet time. Elya has a lot, like, a whole damn lot of patience. If he takes interest in a person he has no problem spending many months gaining their trust. He enjoys it when he can "help" them overcome hardship because when he eventually betrays them, it is so much sweeter for him if they had been ready to give their lives for him.
Dieran is a bit different; sure, he could brainwash someone without his anomaly, but why do so when his power rivals a god?
Talking about his anomaly. Maybe I should try explaining how it works.
It affects the brain like a virus; as soon as the victim is affected, he has complete control over it. He can decide:
-how and what they feel any kind of emotions.
-Take control over all of their senses.
-Heal wounds by manipulating the brain into believing the injury never happened.
-Completely overwrite a brain. Which eventually takes away the victims ability to have their own feelings. They are nothing but an empty host at this point.
-Attach his anomaly to any living being. Just found the beloved family dog again? Well great these people are now under his control.
He caused an unfathomable amount of suffering with the anomaly. Even going as far as taking down an entire small world almost entirely on his own. Simply by going into the minds of the people and turning them against each other. Which ended in a massive war. And when he was done toying with them, he ordered the Chaos Insurgency to deal with the rest.
Do I love writing villains? Hell yes.
Do I want to punch both of them in the face with the force of a truck? Yes again.