I made an account (finally) just to tell you this:
In fighting games, you throw out your special when you RELEASE the final button. In essence, for sub zero's freeze ball, you can press and hold A, do a D, F, then release A. VIOALA! Ice ball!
Now, in your combo, I imagine you are pressing X, A, and then press D, F while still holding A, then you let go of A and an ice ball comes out.
It works for pretty much every fighting game, it is standard for the genre.
Hope that helps explain what is happening.
Actually, that's not really what's going on here. Not saying that it isn't possible to do that in this game, but for whatever reason, there are also "shortcut" specials that you can do without actually hitting the attack button. If the last attack button you hit (in a ground combo, anyway) is the same as the one a special uses, you only have to do the directional inputs to cancel into it. So yeah, you can hit "X, X, back, back" with Scorpion and you'll cancel into his spear. I've even taken my right thumb completely off the controller to be sure.
It's a weird feature, and honestly, I don't care much for it. Occasionally you'll cancel into a special that you didn't want just because you took a split-second longer to hit the button for the special you did want. I'd rather have total control at the expense of cancels being very slightly more difficult.
Actually, that's not really what's going on here. Not saying that it isn't possible to do that in this game, but for whatever reason, there are also "shortcut" specials that you can do without actually hitting the attack button. If the last attack button you hit (in a ground combo, anyway) is the same as the one a special uses, you only have to do the directional inputs to cancel into it. So yeah, you can hit "X, X, back, back" with Scorpion and you'll cancel into his spear. I've even taken my right thumb completely off the controller to be sure.
It's a weird feature, and honestly, I don't care much for it. Occasionally you'll cancel into a special that you didn't want just because you took a split-second longer to hit the button for the special you did want. I'd rather have total control at the expense of cancels being very slightly more difficult.
Look up negative edging.
Imagine if the game let you do crouching MK (letting go of the button afterwards) then inputting down, down-forward, forward to get the full combo (no punch button required after Hadoken motion)