Malcolm Thawne

Malcolm Thawne is another Barry Allen. Well, not really, he is his twin brother. Wait what? Well there is a Flash issue in which Nora Allen gives birth to twins, however at the same time Charlene Thawne loses her baby, because the doctor who needed to deliver it was drunk. And in order to cover his mistake the doctor took one twin and gave it to the Thawne family. Eventually, Malcolm discovers the truth, finds Barry, becomes jealous of the fact that Barry had a better life, and becomes Cobalt Blue, an evil speedster.

Considering how Zoom leaves a trail of blue lighting as he runs, it wouldn't be hard to believe he is Malcolm Thawne. But, then again, Grant Gustin as a villain? Really? This would however, explain what happened to Barry from Earth-2, since he hasn't popped up yet, and it would create a mystery on Earth-1 if there were another Malcolm raised by the Thawne family. It would also explain why he is so hell-bent on killing Flash from Earth-1. On the other hand, it was said that Zoom wants all the speedsters dead, and it was never implied that he has a beef with Barry in particular.