When Jena Malone signed on for a role in Batman v Superman: Dawn of Justice, and then turned up in photos with *gasp* red hair, the immediate fanboy freak-out was that she was playing Robin. Well, no. That was never going to happen and the recent trailers make it clear that's not going to happen, but then if she's not playing Robin, then who is she? Possible spoilers ahead so beware!
According to the latest scuttlebutt from Heroic Hollywood, Malone is playing another notable Batman sidekick, Barbara Gordon. Gordon eventually becomes Batgirl in the comics, but after the Joker paralyzes her in the classic graphic novel, The Killing Joke, she becomes the information wiz known as Oracle. With DC's The New 52 continuity Gordon has recovered from the paralysis and is back on the streets as Batgirl.
Meanwhile, Callan Mulvey's role has also been kept in the dark for a long time, but the general idea is that he'll be playing a bad guy of some kind. Heroic Hollywood once again posits that he'll be Anatoli Knyazev aka the KGBeast, a character that has long been expected to appear. This won't be the enhanced assassin version seen in the comics, either, rather he'll be employed by Lex Luthor (Jesse Eisenberg) to spy on metahumans.
Neither of these are confirmed by Warner Bros. yet, and with eight months until the film arrives there will probably be a lot more speculation to come. Batman v Superman: Dawn of Justice opens March 25th 2016.