Well all the villains are out for the moment except for Phantasm, Ember, Chrome, and Bastion. Bastion has Colossus and Extrusion under a shield so the three of them aren't an option. Chrome and Ember can't really be hit in the back of the head. And Phantasm might be a little risky to fight. That'd be something to see though. Invisible people fight. Or not see as the case may be haha. 

There's also the henchmen who are trying to free the villains. But that's risky seeing as how man of them there are.