In the Foundation area, follow the pathway downstairs to the left of the save station. Two archers will bust through the wall. Throw one of the archer at the wall to the left of the door way and it will bust open revealing a secret room full of lava and a Ying Yang symbol on a ledge. Grab the other archer and throw him in the lava. Then, double jump off the guards back to get the Ying Yang symbol that unlocks Scorpion in VS mode.