Dr. Edward Clariss "“ The Rival

Edward Clariss is a scientist who managed to recreate the formula that turned Jay Garrick into a red speedster. Since, his accomplishments weren't adequately acknowledged, Edward became bitter and resorted to a life of villainy. Which means that, if Jay Garrick is The Flash on Earth-2, Edward Clariss is his Reverse Flash, i.e. his rival. However, I believe this is highly unlikely, since it would be unusual to simply throw a new character into the mix at the end of the season when they unmask the villain.

Sure, we saw the real Eobard Thawne when the first season was near its end, but his identity was only used to clarify how he ended up in Harrison's body, it did not have any groundbreaking impact. In other words, Edward is a viable suspect, but the possibility of him being the bad guy who is suddenly introduced to the audience is very low.