Don't I Know You?G 20

You'll need a second controller to unlock this. It can be done through Free Roam, Free Play or towards the end of the Red Head Detention level in Story Mode. You will need to also progress far enough in story mode to have unlocked both Captain America and the Human Torch.

Simply take control of either Captain America or the Human Torch character with one controller by holding down and then enter the game with your second controller and take control of either Captain America or the Human Torch character (whichever one wasn't selected with the first controller) by holding down on that controller.

The achievement will unlock shortly thereafter.