Which one of those is actually a Green Arrow villain?

Worst in terms of TV performance or worst in terms of damage inflicted to the protagonist?

Have they ever brought Onomatopoeia to the Arrowverse? He is a real Green Arrow villain.

Kind of. There was an assassin named Mr. Blank, but the closest we had to the guy was actually a character on Gotham.

Damian Dahrk

I haven't seen enough of The Arrow Live Action TV series but i choose Dragon

The Ninth circle

Merlyn, he was Better in Season 3