The Batman Beyond post from earlier this year made me realize that the New 52 has affected this site more drastically than I originally thought. No longer can I go on just presuming that past stories still "count", however loosely. They do for the purposes of this site, but in terms of the New 52, nothing exists until we see it again. So I think it's important to take note of what makes it through and what doesn't. And let me tell you...not a whole lot has made it through. Below is the list of everything I could find, and most of it is exactly what you would expect. In the future, if anything else shows up, it'll get a brand new spotlight and a "52 Shakeup" tag, because it's essentially a new character
Harley Quinn first appeared in Suicide Squad #1 (September 2011). She looks like this now, presumably to more closely match her appearance in the Arkham games (2009, 2011):
Batgirl first appeared in Batgirl #1 (September 2011). She's Barbara Gordon again and looks like Batgirl.
Renee Montoya first appeared in one panel of Batwoman #1 (September 2011) and then appeared in one panel of Batwoman #0 (September 2012). That's it so far.
Mr. Freeze's real name, costume, and part of his backstory haven't changed from the Animated Series version. And of course he still calls himself "Mr. Freeze", which is from Batman '66. And, as part of his backstory, Nora Fries is still around..sort of. Her name is Nora Fields, and Mr. Freeze is obsessed with her but they were never actually married. In fact, they never even met. (Batman Annual #1, May 2012)
Clayface is looking more like his animated self than ever in Justice League #30 (May 2014).
The Batmobile's afterburner is still around, but I don't have a first appearance for it.
Presumably this whole page, if the Batman Inc. stuff still counts
Perry White and Jimmy Olsen first appeared in Superman #1 (September 2011).
The Daily Planet has definitely appeared in the New 52, but I can't find what issue. I'm sure it came out in September 2011, though.
Mercy Graves first appears in Justice League #31 (June 2014). She's Asian now, supposedly to match Tao Okamoto in Batman v. Superman: Dawn of Justice, but I don't know which one really came first.
Livewire first appears as a member of the Secret Society of Super-Villians in Justice League #30 (May 2014).
Non first appears by name in Action Comics #23.2 (September 2013), although I've read he appeared as early as Action Comics #5 (January 2012). Interestingly, he appears with Faora instead of Ursa; presumably this is to be more like Man of Steel, but then why wouldn't they use Jax-Ur instead of Non?
Sgt. Casey is mentioned in Action Comics #1 (September 2011). As far as I know, he hasn't actually appeared yet, but he's out there somewhere.
Mr. Mxyzptlk first appeared in Action Comics #15 (December 2012) with a new backstory: he's now a court jester for the 5th-dimensional King-Thing Brpxz of Zrff.
Bizarro first appears in Superman #23.1 (September 2013) as a failed Kryptonian/human-hybrid Superman clone called Subject B-0.
Metallo first appears in Action Comics #1 (September 2011) as John Corben, a soldier under Sam Lane. In issue 2 (October 2011), he joins John Henry Irons's Project: Steel Soldier and wears the Metal-0 suit, The Metal-0 suit is then revealed to be sentient - thanks to a Brainiac virus - and through a series of events, Metallo and Corben become one person and they get a Kryptonite heart in issue 8 (April 2012). Later, they upgrade to Metal-2.0, and then by Forever Evil they begin calling themselves Metallo.
This whole page, except for maybe the Phantom Zone appearance
Giganta's powers, as seen here in her first appearance, Trinity of Sin: Pandora #2 (August 2013):
Green Arrow's costume, as seen here, seems to be a mixture of his Smallville and Arrow outfits. From what I've seen, it tends to lean more toward one or the other based on the artist:
John Stewart's costume, as seen here. John Stewart first appeared in Green Lantern Corps #1 (September 2011).