In Mega Man X, in the Armored Armadillo stage, if you leap up over the door to the boss's room, you find this little slice of heaven.

Pretty worthless, right?

But, if you collect every item in the game, including all weapons, sub-tanks, heart tanks, and body upgrades

Then visit this area several times (the easiest way to do this is to get up here, then leap off to the left into the pit so you start at the halfway point, stock up on lives using this tip)

After visiting this ledge about four or five times a weapon upgrade capsule will appear, and the good doctor will be wearing Ryu's (from Street Fighter) clothes.

Jump in, and you get the ability to throw Ryu's (and Ken's) signature fireball by pressing Down, Down-Forward, Forward, and then the shot button, but only if you have full health.

This thing is able to kill pretty much anything in the whole game in one hit, but you have to be on the ground to use it.

Have fun!