So, a while ago i made a post saying that the Darkin were the main antagonists of league of legends. I was proven wrong, so like the idiot I am, I'm going to try again with a different approach.
1. The Void
The Void serves as Leagues "Eldritch Horror" area and packs a pretty bug punch. With its Endless Army of Voidborn and The mysterious Watchers leading it, the void is a pretty good candidate for Supreme villain. It serves as the main antagonist of Freljord, and Shurima (via Icathia). Its Current Goal is the Destruction of all existence.
Pros: Unending Ammount of Voidborn, Unkillable, Omnipresent, Can adapt to any situation
Cons: Needs time to adapt, Watchers cannot enter Physical Realm without Immense Preparation,
Leagues "Demon" champions. 5 incredibly powerful Ascended who were sealed in their own weapons with Targonian Magic. Their Current goal is the Destruction of all existence.
Pro's: Unkillable, Experienced in Blood Magic, Extremely Powerful
Cons: Most are Currently Trapped in their weapons, Can be overwhelmed with a numbers advantage
This is pretty much the best the best competitor for the title we have had yet to see. He Is leagues "Plans within Plans" Character, going as far to plan for his defeat and rely on it as part of his plan. His Current goal is Activating the Immortal bastion to Rebuild the afterworld in his image.
Pros: Unkillable, Extremely powerful Necromancer, Physical Strength, Army of Spirit warriors
Cons: Not much, other than the fact that he is currently trapped in the Death realm.