“First announced back in June, the “Dimension Shellshock” DLC for TMNT: Shredder’s Revenge is out now on consoles and PC. The $8 downloadable content adds two new playable characters, a co-op survival mode, and additional color palettes for each character. These additions will add new life to the game for experienced players, especially those who like a challenge,” says Co-Optimus.
Source: N4G PC TMNT: Shredder's Revenge 'Dimension Shellshock' DLC Co-op Review [Co-Optimus]