After The Flash and the Reverse Flash fought each other in the year 2000, the Reverse Flash was seen losing his speed. Gideon (who surprisingly has not been seen at all so far in Season 2) informed the Reverse Flash that the jump in time drained his powers.
But maybe there was more to that. Perhaps prior to the great fight, the Flash and the Reverse Flash felt the need to set aside their differences and team up to work on a major problem: Zoom.
It is possible that Hunter Zolomon, Zoom, wanted to become a speedster. In order to do this, he decided to take up the mantle of the Black Flash. This would explain Zoom’s demonic characteristics.
After becoming the Black Flash, Zoom became insane and wanted to absorb the speed of all speedsters in all timelines and kill them. He feeds off death and the more speed he absorbs through his fingers, the faster he becomes. This was such a problem to the Flash and the Reverse Flash, that they were forced to work together to take down Zoom.
While the Barry and Eobard were working together on Zoom, Barry revealed his identity to Eobard. But during an intense fight with Zoom that included Barry Allen, Jay Garrick, and Eobard Thawne, Thawne felt that Barry used him as bait to take down Zoom. This resulted in Zoom sucking some of Eobard’s speed away from him.
They then thought that they had defeated Zoom and Jay Garrick left. Eobard was furious with Barry and got into a massive fight with him. During their fight, the Flash and Reverse Flash time traveled, resulting in the death of Nora Allen. Due to the speed that was sucked out of him, Eobard’s grip of the speedforce was weakened and collapsed after time travel and a nasty fight with the Flash.
As a result of their time travel, the two speedsters disappeared from that timeline. This prompted Zoom to travel back in time as well. He started in Earth 2 and took out Jay Garrick. Earth 2’s particle accelerator was likely meant to explode at that point in time, whereas Eobard altered the timeline for the Earth 1 accelerator to explode. Now that Zoom has found Barry, he wants to finish him.
Using the resources that the Black Flash has, he knows Barry’s identity and everyone that he works with. He can see through time, and therefore, could easily take down Barry Allen. However, Zoom is still human enough to want the glory of dragging out his fight with Barry. This is why Zoom doesn’t just travel back in time and kill him. In addition, the faster the Flash is, the tastier his speed is. This also why Zoom sends over metahumans to fight the Flash. He wants his prey to be as tasty as possible.
Zoom will probably be thrown a curveball when he meets Wally West, who he was not familiar with in the timeline that he originated from.
Seeing how tough Barry is to beat, Zoom will probably travel back in time and restore Eobard Thawne back to life. He would do this by making Eddie appear to have died, replacing the suicide bullet with a device that gives Eddie the appearance of death. Then he would move Eddie into the future, making Eobard Thawne come to life later in time, without altering the current timeline. Eddie would then become Malcolm Thawne. This would create a different version of Eobard Thawne on Earth One than the one that killed Barry’s mother. This Eobard Thawne would theoretically be born a few centuries latter and therefore, be more resourceful. He could potentially use speedforce technology in addition to his speed.
By recreating Eobard Thawne in this way, Zoom will still be able to feed off the current Barry Allen and his tastier advanced speed. It will also give Zoom insurance, he figures that Eobard and Barry were enemies, so he could work with Eobard to take down Barry. After taking down Barry, he would then go after Eobard as revenge for the original Eobard coming after him, as well as for his speed.
But three Flashes and Jesse Quick will take down Zoom before Eobard Thawne travels back to the 21st century. This could also change things a little, because after finishing off the threat of the Black Flash in Season 2, the Flash would probably start over with a normal Zoom and a different version of the Reverse Flash.
Personally, I doubt that any of this will become true, but I do think that this would make things very very very interesting.