That's pretty much why I put Dimentio first.I believe Dimentio is the most evil.
Dimentio has no allies but himself. Every other villain in the series has had minions who support them, SOMEONE who believes their goals are worth working toward, but Dimentio has no minions, he just poses as one. None of his allegiance is sincere, he cares for himself and himself alone. Everything he does involves stringing others along who are unaware of his true intentions, he often seems to be pals with the other minions of Bleck but it's all a facade. He doesn't bat an eye as he casually discards anyone he has no use for anymore.
The Shadow Queen is the closest to him in terms of evil, and she is more powerful in her base form, but she is non-hostile at least toward Beldam. That's what gives Dimentio the edge imo, he lacks true concern for anyone other than himself, has no loyal minions other than those he forcibly brainwashes, and will totally rewrite existence to put himself on top, anyone else (including the rest of Bleck's team) be damned. And that's why I love him so much.
If Nintendo did that I would yeet my 3DS in a lake because nothing would be worth playing anymore.I would absolutely love to see a battle between Dark Bowser & Dark Fawful Bug, and Super Dimentio.