Cruising the Ubisoft Twitter, as we are wont to do, we stumbled upon this little update. According to said update, registering TMNT: Smash Up with Ubisoft will grant players access to a code to unlock Shredder and Cyber Shredder as playable characters. Checking out the veracity of this claim -- as we are also wont to do -- we discovered that the official Smash Up site has already publicly posted the code.
We're not sure where the marketing wires got crossed, but it benefits us all, so we're not complaining. To perform the unlock, select the Bonus Content option and enter the following: Up, Down, Right, Up, Down, Right, Left, Up, Right, Down. Don't get to excited, though. Cyber Shredder is just a different costume for normal Shredder, so don't expect a whole new character to flesh out the game's unfortunately puny roster.