Very mild spoiler warning in case you haven't seen the end of the last episode of the Flash...Please STOP reading if you don't want to be spoiled on who returns...
You have been warned...
Still with me? Ok, then. Let's get on with it then.
So, the writers did one of the biggest mistakes ever in my opinion and that was bringing back the Reverse Flash after he was erased from existence in the season 1 finale. That's a death NO ONE can come back from, that is a PERMANENT thing folks. And yet, here he is defying all odds and has magically returned when he shouldn't even exist!
I complained about the opening of Flash season 2 because if Reverse Flash ceased to exist then Barry's mother should still be alive, Harrison Wells should still be alive, Barry shouldn't be the Flash, etc, etc, and yet the writers didn't reboot the timeline when by all rights, they should have because time SHOULD work that way. It's called cause and effect and there was none and that is why the first episode of this season of the Flash didn't work for me.
And now this...the return of a villain that, by all rights, shouldn't even exist.
Alright, I've ranted long enough., I apologize for that. Onto my theory...
Like Daveym said, I will cling to this until the bitter end and until I am shown in an episode of the Flash with CONCRETE proof that I am wrong.
Eddie Thawne is alive. This is the ONLY way the Reverse Flash can still exist is if Eddie himself is still alive.
Yes, we saw Eddie kill himself, and yes we saw him die and then Reverse Flash gets erased from existence. Why? Because Eobard Thawne is Eddie's super great grand-child from the future, that's why. And without Eddie Thawne, Eobard Thawne cannot exist.
Then after Eddie died, we saw Eddie's body get pulled into the singularity. Now, since I have already recognized the fact that Eddie Thawne is a lot like Hunter Zolomon (both were cops), it's not out of the realm of possibility that Eddie could have been put onto Earth-2 and got revived somehow due to some scientific experiment. And since a singularity is often associated with time travel, it's also not out of the realm of possibility that Eddie could have ended up somewhere in Earth-2's recent past (say, 3-5 years in the past).
Now, since Eddie and Hunter Zolomon have a lot in common (remember, both were cops), I believe more than ever now that Eddie Thawne and Zoom are one and the same (Eddie just moved from the bottom to the top of my list). Perhaps that scientific experiment brought Eddie back from the dead. Perhaps that same experiment means he cannot ever take his suit off as Zoom because it keeps him alive. If the suit keeps Eddie alive, this could explain why we haven't seen Zoom take off his mask.
Think about it. Eddie knew Barry was the Flash and straight from season 2's first episode, Zoom starts sending meta-humans at Barry. The timing couldn't be more perfect and is very suspicious.
Also remember Harry admitted he created Zoom. Perhaps that scientific experiment I mentioned earlier was the very thing Harry used to bring Eddie back from the dead and thus created Zoom. And it's not out of the realm of possibility that Eddie could have found himself in a different world without Iris, without a job, without anything and blame it all on Barry. Like I said, the timing is perfect, too perfect.
I'm calling it right here and now, Eddie Thawne is Zoom! But even if Eddie is not Zoom, he's definitely alive and I'm sticking to that until I am clearly proven to be wrong.
My theory also leads to an inevitable question. Why does Eobard Thawne hate Barry so much? In the comics, Eobard is a huge fan of the Flash/Barry Allen. So, he conducts scientific experiments on himself to gain speed and it works. Then, Eobard wants to meet his hero, so he goes back in time to meet Barry but he arrives just a little too late and finds that the Flash has died years ago. Eobard's hero worship is shattered when he finds out that Barry kills the Reverse Flash (Eobard Thawne) by snapping his neck in order to save Iris West. From then on, Eobard hates Barry with a passion.
But in this TV show, Barry doesn't kill Eobard, Eddie does by killing himself and causing the Reverse Flash to be erased from existence. So, with that in mind, I ask again: Why does Eobard Thawne hate Barry so much? Eddie is the one that made sure Eobard never existed, so it is HE that Eobard Thawne should hate not Barry.
Well, there's my theory and I'm sticking to it.