It's same thing like with Robin. She technically debuted as a villain working for Crocodile. But after that arc she became a hero. In a sense Du could also say she's a neutral character.
He's not a great villain although he is still a villain and entertaining af. He's like a knock off, whiny, immature version of Patrick Bateman (American Psycho) and it's hilarious.
I have too many of them. Most of my Favoriten tend to either be antiheros oder villians of some sort
But lets play "off the oben, nach oben of my head"
Misogi Kumagawa and Akashi are often considered antagonists, at least for a point of time. Kuroha is amazing too, Hanbei Takenaka, Hisui Nagare, gin Ichimaru, Pride, Mary from Ib, Marluxia, Saix, Xigbar, N, Ferid Bathory, L / Light, Alone / Hades.... the Liste goes on and on
i don't like villians but uuuh if i ever liked villians i guess it would be light yagami from death note and sheogorath the mad god (demonic god) and yes sheogorath is the one in the picture.