This game, just like the last, has a secret Street Fighter move that you can unlock if you get every collectible in the game. In the second Sigma stage, once you get to a fork where you can go up or down a ladder, use your ice shot to freeze the bat and climb up the ladder at the top. Pass the obstacles, and when you are falling down, hang to the left. If you make it without losing energy (you can use an energy tank), there should be a Dr. Light capsule that will teach you the Shoryuken.