The plan was, and may still be, to have Joe Manganiello the main villain The Batman film which Affleck was co-writing and directing at the time. Affleck left those positions with Matt Reeves taking over as writer/director on the project and when he did, Deathstroke being the villain seemed increasingly uncertain – especially as Affleck’s involvement became questionable.
Where The Batman stands at this point is also not clear. But Manganiello tweeted the the first official still of himself in character filming that scene
— JOE MANGANIELLO (@JoeManganiello) November 25, 2017
