Villians in Runeterra

The ones seen as heroes could be the most evil of all

What about ?

Swain is the leader of Noxus, his people would not think him a villain. LeBlanc also is a bit more gray than you are giving her credit. Sion was remade to be an immortal soldier for Noxus, again Noxus would not see him as evil/villain. Vladimir is an interesting case. But again Noxus would value some of his traits.

Elise would fall under villain, she simply wants to kill to preserve her beauty and youth. She is not valued by Noxus.

Camille is definitely not a villain. She is an enforcer for one of the Piltoven Houses. She is the definition of morally gray. She skirts the lines a little but for a cause that is just in her eyes.

Viktor literally tried to steal something from Jayce. Urgot is a villain to the villains, but still is breaking the law so remains a villain. Warwick is the same deal, but has a more sad story after the rework. Mundo is insane, but villainlike. Singed is potentially villainous.

Jhin is deranged murderer used as a weapon by the good guys of Ionia. Zed and Syndra would fall under villain, yes. Kayn by extension. Xayah is not she is a rebel in a sense, but Zed is one of the major players against her. So I wouldn't count her as villain, just a minority viewpoint. She wants to free the wild magic, which Zed, among others including "good" Ionians, capture and steal.

Brand is the embodiment of fire, probably villainous, Lissandra is Ice Witch, and a scheming villain. Sejuani and Olaf are just a more warlike side. Olaf did fight the Mist. Sejuani disagrees with Ashe and wants the freljord to go back to more warlike values and become strong. I wouldn't call her a villain.

Shurima is on point, Xerath is a villain and Renekton is a fallen hero.

Aurelion Sol hates all of Targon because they captured him so at the very least he is vindictive.

Evelynn's motives are more difficult to pinpoint I think.

Graves and TF aren't villains, just thieves and swindlers. I don't think they would be any more a villain than Miss Fortune. Gangplank is similar, he just represents a different side.

Aatrox is the aspect of war, the people he is on the same side might see him as a hero, but on the opposing side they might see a villain.

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I want to add also and

Basically, Cassiopeia is a sadistic temptress, Jinx wants to destroy things and loves Chaos, Morgana is kind of an evil witch, Vayne is now a shadow huntress, but she has no more empathy and likes to make suffer and Zyra is a predator who feeds on her prays.

Morgana prevented Kayle from committing genocide on many worlds. So going to safely say you're wrong there.

Same with vayne.

Cassipeia is more dynamic than that, she is Katarina's sister using guile instead of assassination to accomplish the wishes of her House and secure its place in Noxus. Her family would not say she is a villain.

Jinx is an anarchist, anarchy is not necessarily villainy. Villainy implies motive and for Jinx there is no motive.

Morgana just feels like Kayle is a supremacist and wants to kill her. Also both Kayle and Morgana are due for lore updates so this one can't be too in stone either way.

Vayne is essentially batman, but more zealous. She wants to kill everything evil, and like most Demacians she despises magic in general. She is closer to an antihero not a villain.

Zyra would fall under villain sort of, but only as much as a lion in the wild would. She just eats mages. If you call Zyra a villain then so is Rengar.

Villainy is a difficult concept and more characters in League Lore are gray than anything else.