Some of the names in this regard that are being thrown around are Captain Cold and The Trickster. It could turn out to be someone who is completely new to the series and chances are there too that Barry could be facing an Alien threat in the upcoming season. All being said, nothing can be confirmed until the showrunners come forward with some concrete news regarding the matter.
A renowned website reports that the third season might see the Black Flash making an appearance. During the last episode it was seen that after Barry defeated Zoom, the demonic Time Wraiths appeared and took him away with him.
During that process, Zoom’s body and his suit were seen deforming. His body was seen disintegrating and he somewhat looked like the Black Flash before he was carried away by the Tome Wraiths through the portal.
This could trigger the storyline for the upcoming season as Zoom could come back as the Black Flash who is basically a Grim Reaper for speedsters. His sole purpose is to kill speedsters and take them back into the Speed Force.
It will be interesting to see how Barry reacts if the enemy that he has already defeated reappears with the sole purpose of killing him once again. The Flash will return to TV this Fall.
Stay tuned for more update on The Flash: Season 3.