So I knew I'd seen her somewhere before, but the woman on Nimble Strike (Tachyon) also appears to be the woman on Uncharmed Life (Setback). In both she's surrounded by mirrors, and the beam she's shooting at Setback appears to be fire or energy based.
Edit: Oh, and High Risk Behavior (Setback) too.
Edit2: Looks like her on Hyperactive Senses (Naturalist).
Anyone spot her on any other cards? Theories, rambling, etc?
Mirror girl is also in the Naturalists deck on Hyperactive senses. Naturalist seems to be looking at that Mirror Girl as she is doing the old Pokemon "Double Team" move and Naturalist is sensing the real one. Great artwork for that one.
Ambuscade seems to have enlisted the help of a mysterious crew as shown on High Risk Behavior. Mirror girl looks to be a part of that little posse.
Also, the mirrors are probably not actually showing reflections, as the one above her in High Risk Behavior is reflecting her front (like the others) instead of her top (like a real mirror)
Based on the fact that she's everywhere, I'm assuming she'll be important. Maybe have her own villain deck? If I had to take a stab in the dark, she might be a mini-expansion, and possibly Guise's nemesis. That's my impression of her.
For anyone who doesn't know, this character is obviously meant as a reference to the Mirror Master, one of the Rogues who persistently oppose The Flash in DC comics. Since Tachyon is a Flash homage, "Mirror Mistress" was clearly included in the art of one of her cards as a reference...I didn't expect to see her again. But perhaps her inclusion in the SOTM storyline will be something cheaty, like how Treacherous Ape (a clear reference to Gorilla Grodd) is pictured on one of Tacky's cards, but appears as a Projection in Dreamer's deck...where Tacky recognizes him, so presumably this is not his first appearance and she knows that he's out of place in the dreamscape. Thusly, while there was presumably a "real" Treacherous Ape, his only representation in the card game (aside from art) is actually an illusionary duplicate of him, not the real him. And Mirror Master is also big on creating illusionary duplicates....
I'd also add in quite a large dose of Mysterio, especially given she seems to be part of Ambuscade's equivalent of the Sinister Six more than a Rogues team.
FYI (for everyone's benefit): If a character is on a card, you can bet we'll find out who it is - they have set up every character and know who they are and where they are from. 
I'm personally excited for "Slice of Pizza Man" who is really angry at Tachyon for what she did to his brother.
PIzza the Hutt?
Right, because the guy on Wraith's Combat Stance can't possibly be just some random street punk. He MUST be a unique and special character with his own particular place in the canon, right?
Yes.
Doesn't mean he's important, but it does mean he's not just a random character created for the card art. The art represents actual events in the comics.
That's not the same thing as what you said earlier. You were implying everyone WAS important. If Combat Stance can depict a random punk, why couldn't Nimble Strike have depicted a random super-punk? (If the character shows up again, in Vengeance art, as you say, then fairly obviously that's not the case, but before Vengeance info, it could have been.)
I talked to my sources, and yes, EVERYONE is important, especially that random street punk. Certain sources confirmed that criminal is The Center--the living embodiment of The Cosmic Being. So there. They've been hiding him in plain sight all along. Satisfied?
EDIT: Niel's right.
Evandan, I'm guessing you're being sarcastic but I'd be careful. If using the words "Christopher told me"becomes a trend for sarcastic humor, it may be hard for people who actually have confirmed stuff by talking to Christopher to be taken seriously.
I see your point–sarcastic comment changed.
"Christopher told me" something, but it was a secret, so I'm not telling any of you.
(It involved Waffles and the End of the Universe, I didn't listen to the second part though, I was thinking about the waffles)
Once more does the siren call of waffles doom mankind. Willwe ever learn not to fall for the sweet and buttery temptations of these misshapen pancakes?