Naomi. That would be a twist.
Ace the Bat-Hound.
Evil Alfred on a killing spree.
Starfire
Barbara Gordon
Alfred
John Constantine
I’m going with Alfred. He knows too much.
Lana Lang
Lol.
An evil Jimmy Olsen would just be tragic
Ambush Bug with Cheeks The Toy Wonder.
the teen titans go version of robin.
Swamp Thing
I’ve always felt it’s someone like Shazam or Supes. It isn’t just that they’re the biggest kids on block in terms of power, but also what it means for them to fall. Like, in a world where one of them breaks bad what hope is there for anyone else?
Krypto
supergirl
I guess no one else wants an Evil Martian Manhunter? In terms of an Marvel character powerset, part Vision, part Skrull, part Prof X. And for DC characters, detective skills akin to the Dark Knight and orbital flight capabilities like the Boy Scout. All that wrapped up in a nice, neat Evil package. Mental possession via Gorilla Grodd? Starro? 
Evil Wonder Woman
Ma Hunkel!