coyote6
Adventurer
Add other big enemies picked from the heroes with large rogues galleries, or add villains that are ubiquitous, but not an archenemy of any one hero (or at least not one of the heroes featured) -- for example, Deathstroke. Not really the archnemesis of any one hero, but there aren't a lot of heroes he hasn't faced. (Plus, he's had his own comic before, and basically has one again now.)
Darkseid might be another option, if you wanted a really big bad evil guy to be included.
Darkseid might be another option, if you wanted a really big bad evil guy to be included.