Ben Affleck who is currently in London reprising his role as Batman in the “Justice League” movie just shared a video of some live-action footage featuring the villainous assassin Deathstroke on the Justice League Movie Set.
— Ben Affleck (@BenAffleck) August 29, 2016
The identity of the actor playing Slade Wilson/Deathstroke is still a mystery for now but speculation is, and The Wrap is reporting, that this Deathstroke video is test footage from the Batman Solo movie that Affleck is directing.
The DCEU has shown that they’re willing to drop their characters into other movies to give the cinematic universe a feeling of connectedness ala Marvel (ie. The Flash and Batman in Suicide Squad). Whether Deathstroke will be making his DCEU debut by showing up in the Justice League film before taking on the Dark Knight as the main Antagonist remains to be seen.