Okay here's the deal with Killer Frost and Captain Cold in Injustice.
Captain Cold has Evidence, Killer Frost doesn't. That achievement pic is probably the only thing leading into that Speculation.
I know some people won't take me seriously because I'm Captain Cold fanboy, but whatever I'm just trying to defend him
Let's Look at the evidence
The Ice Beam shooting the Flash in the announcement trailer
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I know some people will say "But, that could be any Ice Character" or "It doesn't even look like ice"
I've seen Killer Frost manipulate ice but never seen her blast it in a beam form before.
Captain Cold heavily Resigned in the comic.
Uh, I don't think they would give him a huge Redesign just to give him 1 or 2 appearances in a comic.
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Every major Justice Leaguer has a villain of their own in Injustice
The only ones left are Flash and Aquaman.
I don't think Doomsday will have a slot on that roster we're currently seeing. He'll most likely be Unlockable, but not in any of those slots we see (it's what I'm guessing. So it might be three slots
Which leaves room for Both a Flash and Aquaman Villain
Unless it's true that the roster is more than 24, but from what I keep reading no one is 100% sure.
Killer Frost Evidence
Just this...