How I think evil works:
To do something truly evil you'd need to create a character beyond the scope of comprehension - doing so, often, comes across as distasteful. They live in their own little realm with incomprehensible thoughts and, usually, the path to get their is one laden with tragedy; these tragedies are, usually, a reality for some people and are largely misused without any general direction of cause-and-effect. I see it a lot of time, not so much on the board, but in literature and movies, where the villain is evil because "bad things happened."
When you see an excellent villain portrayed in any media, not all of them are evil, per se - there's a distinct difference between being evil and bad; one of the most important factors tends to be an archetypal sacrifice of their identity. Who they once were (think of any truly
evil character or figure whose sole purpose was destruction), an integral part of the transition from bad, wherein they operate off of need and instinct, but still maintain a sympathetic character because they are, ultimately, just trying to fufill their desires in some way - just like the rest of us. However, when that fufillment turns into successful self-destruction (Darth Vader losing all he had that tied him to his humanity: his body, his wife, his children, his name, his friends, his mother; you can see this pattern repeating into multiple evil villains, even if you don't know who or what they were before the self-destruction phase: e.g. Sauron, Hannibal Lecter, etc.) in that moment, every aspect of who they are is evil. This is also seen in religious figures (think Lucifer, when he falls from grace), stories (Jack Torrance, how he tries to kill his family), and so forth.
I'll be using Darth Vader as an example from now on, since he was wholly based of Joseph Campbell's archetypes.
However, what distinguishes these figures from simple devil-figure archetypes is the depiction; whether or not you reveal their downfall can help build sympathy towards the character and ultimately change their direction. There are strengths and weaknesses to starting off your character in different stages of the story, whether when they were innocent (what George Lucas attempted in Episode 1 with a young Anakin Skywalker), to when they were attempting to fulfill their needs (what George Lucas attempted in Episode 2 with Anakin trying to control his feelings), to their downfall (obviously an Episode 3 Anakin), and finally the embodiment of evil they've become (when Anakin transforms into Darth Vader). When George Lucas tried to backtrack on his development, by attempting to restart his depiction at the earliest stage, adding sympathy to a character we've held no such feelings for until, in the end, what he had destroyed was returned to him (his son saw him again as Anakin Skywalker and, in the end, Darth Vader had family again - effectively undoing all the destruction he had wrought on himself); ultimately, it didn't work - the entire process of development became unbalanced and even.
By creatively interlocking these stages of development, it isn't simply cliche, because they reflect human nature, and ultimately helps to build a character who is evil but sympathetic. It allows them to be dynamic and thoughtful, but still cruel and dark, kicking puppies and blowing up planets.
However, by starting off a character as evil, you need to be careful if you backtrack; as long as you don't spill the beans all at once. Or, alternatively, you could remove all intent of making them remotely sympathetic - let them be evil as can be, provide minimal reasons - that also works well, provided you have a strong foil (a character whose the opposite of yours - in this case, think of a
protagonist) who can carry the weight of two character's worth of sympathies.
In the end, evil works - it's just a matter of tact and understanding the dynamics, how it relates to yourself and others as human beings, as well as being passionate about the portrayal. Evil characters need to be thoroughly evil to maintain the haunting, gravitational pull of despair - again, with Darth Vader; he remained stalwartly evil until the events that led to his self-destruction were undone. That's why, I'd imagine, for a lot of you, it felt kinda cheesy at the end of Episode 3 when he started screaming and crying - he was past that point of development, and clearly felt out of place. In the long run, keep in mind what you want out of your antagonist and stick to it.
That's my thoughts on the subject - I might've been rambling for a good portion of it, but it feels good to get my thoughts out there. Someone might make something of it.
TL;DR - My character isn't evil. He's in the process of becoming evil.
