A set image features Kid Flash side by side what may be Black Racer from the DC Comics, with a second image featuring Grant Gustin as Barry Allen.
Black Racer, in the comics, is the grim reaper of the DC Comics and the bringer of death. It's basically his job to collect souls from the dead.
Grant Gustin did tweet out that the main villain of The Flash Season 3 isn't a metahuman, so technically Black Racer fits the bill.
We did see Black Racer (Black Flash) potentially in the Season 2 finale when Teddy Sears' Zoom was killed off.
With Barry going back in time and messing with the timeline (Flashpoint), it's possible the Black Racer could show up to take out all the Speedsters -- including Barry and Wally (as they are not supposed to exist in the new timeline).
We may find out more next week as The Flash will be featured at Comic-Con.
Regarding whether or not Zoom plays a role in The Flash Season 3, Tom Cavanagh seemingly teased the character might play some part.
The Flash Season 3 returns Tuesday, October 4th at 8pm ET on The CW.
Black Flash from The Flash Season 2 finale: