Well it looks as though work on the next Batman movie is starting to gear up, and Ben Affleck (star, co-writer, and director) has given us our first look at the film's villain: The Mercenary Slade Wilson, aka Deathstroke.
— Ben Affleck (@BenAffleck) August 29, 2016
It's not fantastic quality, given that it seems to be someone filming footage on a screen, but it does give us a good look at the character. I'd assume it's legitimate, unlike Henry Cavill's black costume tease, because it seems like far too much effort to put into an elaborate prank.
The Wrap is also reporting that Deathstroke will be the main antagonist of the Batman movie, but we don't know who the actor behind that mask is (rumour is that it's Welsh actor Julian Lewis Jones). We also don't know if this is test footage, a cameo scene from Justice League, or an actual scene from the yet-untitled film.
My guess would be the one of the first two, since filming on Justice League doesn't seem to have finished yet. Surely Ben Affleck is a bit tied up to make a proper start on anything other than pre-production on the solo film.
This wouldn't be Deathstroke's first time in live-action, as fans of Arrow will remember him as he main antagonist of season 2 (played by Manu Bennet). It would be his first appearance on cinema screens, and fans will know he's more than a worthy adversary for the Dark Knight. [io9]