In Single Player/Ko-Op:
Available in Versus Mode Only
In Versus Mode Find the Red Yin Yang in The Wu Shi Academy. After you open all the water switches to put the fire out in the Wu Shi Academy, drop back down to the ground level. Get on top of the house with the spiked ball. Then look for an opening with a spiked ball in the tower you just jumped down from. Inside that opening is a Red Yin Yang that unlocks Johnny Cage in Versus Mode.