You might remember a while back that we talked about getting a Ha-Do-Ken for Mega Man in the first Mega Man X game. So, it might not come as a huge surprise that there's a similar secret in the second Mega Man X game.
The conditions you have to meet are similar. You have to have found all of the E-Tanks, heart tanks, Zero parts, and sub-weapons. Basically, every collectible in the game. Then make your way to the third Fortress stage. You'll eventually find a ladder up high enough that you'll have to lure some enemies over and hit them with the Crystal Hunter to make platforms.
You'll have to then traverse a kind of treacherous path, with some pretty tough spots.
Once you get to the vertical shaft, hug the left wall to enter a hidden passageway to find a weapons capsule!
Inside is Dr. Light, who is apparently a big fan of Wayne's World.
Hop in and you get Street Fighter's Ryu's signature move, the Sho-Ryu-Ken!
Which you execute by pressing Forward, Down, and Down-Forward + Shot. It looks kind of cool, but you get it at nearly the end of the game, so you don't get to school very many bosses with it, and its range is so short that you'll probably get hit before you get a chance to actually hit something with it.
But, hey, don't worry about that!