Dear 100 Hour Board,
What type of villain is the most evil:
1) The villain who doesn't believe in the concept of good and evil.
2) The villain who believes that evil is good, and good is evil.
3) The villain who knows the difference between good and evil, and willfully chooses evil.
What are some examples of villains who fit into these categories?
Definitely number three. Prime example: Lucifer-->Satan.
Guess what? Kingdom Hearts has examples of all three! I don't answer questions often so I'm going to give you a nice description of all three of these.
Here's a primer on Kingdom Hearts lore that will be relevant to the list you asked for. When a person gets taken over by darkness, their "heart" (meaning soul) leaves their body, gets overwhelmed by darkness, and turns into a Heartless (ironic name, I know, but bear with me). A heartless is a creature of darkness that has no emotions or thoughts, it just acts on instinct to try to create more heartless. When the heart of a person leaves their body to become a Heartless, their body animates and becomes a Nobody (also ironic, but bear with me). That Nobody is also emotionless and only acts on instinct. Now these rules apply to everyone unless they have a "strong heart" in which case their Heartless and Nobody retain their memories and will though they also get their own personalities sometimes.
Now Kingdom hearts is not very subtle in saying Darkness is bad and Light is good, so keep that in mind as you read the next part.
- Xemnas is a Nobody that was created when Xehanort was overtaken by darkness and his Heartless became Ansem Seeker of Darkness while his body became Xemnas. Xemnas knows there is light and darkness in the world (good and bad) but he rejects both of those in favor of something in between called Nothing. He believes that Nobodies are manifestations of Nothing and that Nothingness is stronger than the power of light or darkness. He's a pretty bad dude and tried to take over all worlds in the universe by...doing....stuff....with lots of hearts? Basically he wanted to destroy the universe's light and darkness and turn everything into Nothing. It's actually not that clear how he was trying to accomplish it but he basically rejected everyone else's morals of good and evil and created his own.
- Ansem Seeker of Darkness was Xehanort's Heartless. He and Xehanort both agreed that a heart's true nature was darkness (evil). So he did experiments on different people in order to create more Heartless and try to engulf the universe and all Disney worlds (!) in darkness. He didn't necessarily think that light was bad, but just that light was weak and unnatural. Why try to be good when your nature is already evil? He caused lots of pain and suffering for every character in Kingdom Hearts so it's pretty clear why he is a bad guy.
- Vanitas is not related to Xehanort directly (woo!) instead he was originally part of the heart of a nice boy named Ventus. Everyone has some light and some darkness in them (except for a few special people but that's not relevant here) so Xehanort did some experiments on Ventus and extracted all the darkness from his heart. That left Ventus as a boy with no darkness in him and Vanitas as a boy with no light in him. Vanitas was a very, very bad person because he thrived on negative feelings like hate, physical and mental pain, and loneliness. He was never whole because his heart was literally torn apart meaning Ventus and Vanitas each only had half a heart. Imagine if you only had half of your emotions. If you could never experience both pain and joy, both happiness and sadness, you would be pretty messed up. Anyway, Vanitas was bad because he didn't want to kill anyone or take over the universe or anything like that, he wanted to hurt people everywhere and that's it. He was emotionally manipulative and hurtful in every way he possibly could because that's all he knew. He was constantly in pain because that's what he was born out of. And when he was given the choice to try embracing light and giving up his pain, he rejected it and chose to remain in his dark, lonely place.
Ultimately I agree with Anathema by saying that the third option is the worst. Using my examples above, all of these people were bad but Vanitas was the worst. I mean, Xemnas wanted to destroy everything and Ansem wanted to convert everything in the world into mindless creatures of darkness but if they would have accomplished their plans then no one would be hurting anymore. Everyone is dead or everyone is mindless and emotionless. Vanitas wanted the world to keep spinning, for life to go on but to torture people with negative emotions and pain forever, very similarly to Satan, and I think that makes him the worst of all.