I can land this move nearly every time. I hope I can help some of you figure it out, too.
I practiced for 2-FREAKING-HOURS to try doing this move consistently. I couldn't do it ONCE for the first 45 minutes. Once I was able to do it, I found I couldn't do it consistently since the timing was so small. Eventually, you have to train your hands for the timing: the window is just too small to be able to think about it as you're doing it.
***I HAVE TAP UP TO JUMP SET TO
OFF ON MY CONTROLLER (Z is Attack, C-stick is Smash). IT'S SUPPOSEDLY PERFORMED DIFFERENTLY FOR TAP UP TO JUMP PEOPLE***
The gist of the technique is the following: Sheik accelerates greatly when she first dashes. By cancelling the dash animation, you are retaining her momentum in the direction she was accelerating but simply choosing to do an up-smash instead of the dash part. So, what is really happening?
You're dashing forward by moving the control stick to left or right.
You're hitting the C-stick DOWN to dash attack (even though it's set to Smash)
You're IMMEDIATELy cancelling that attack with an Up-Smash by smashing UP+Z.
Final result: You're UP SMASHING with Sheik's DASH ATTACK momentum.
Below are the various ways I've been able to perform the move. I find the easiest way to learn using this method is try charging the smash by holding the Z attack instead of tapping it. I also smash the C-stick down instead of flicking it down until I see the move come out. It seems to be SLIGHTLY more forgiving with the timing when you do this. Either that or it's just my imagination and it makes it easier to perform for me. Whatever works...
The Easiest Way (also the most unreliable)
According to what I stated earlier, you start off running then up-smashing. Most ways of performing this technique require very tight timing on the control-stick when switching the direction from left or right (the dash) to straight up (the smash). HOWEVER, I discovered that you can alleviate the need to even move the control stick during the cancel, although it is inconsistent (works sometimes, doesn't work other times). If nothing else, I say if you can't do the normal method yet for executing this tech, try starting with this:
Assuming we're doing this to our right...
Hold the control-stick to the Up AND Right to make Sheik Dash. It's tricky to actually start the dash sometimes doing this so it helps to move it more right than up (at least initially).
While holding that direction, press Down-C IMMEDIATELY FOLLOWED by Z-attack The timing is so close on down-C and Z that it looks, feels, and sounds like you're doing them both at the same instant. If you're having trouble timing them, try pressing both at the same instant and you'll eventually get lucky and nail the timing.
PROS: This is the easiest way to do the tech. It's just holding one direction (UP-RIGHT) and pressing two buttons at roughly the same time.
CONS: Inconsistently starts the dash when going UP-Right sometimes. Sometimes no matter the timing you're holding the Control Stick too far to the right and she never goes into the up-smash. Still, if you're at wit's end with this tech, I recommend you try it this way before giving up to see if you can grasp the idea better.
Harder Way (more reliable)
Same buttons used but with one stipulation: we're saying, "screw the timing". We're going to be moving the CONTROL stick in two directions, and pressing two buttons. Let's do it.
Dash to the right. Simple. We're just holding the CONTROL stick to the right.
At the SAME INSTANT you press UP on the Control Stick, you're also pressing the C-stick Down and Z button at the SAME TIME.
This is unreliable because, as I stated before, the inputs are NOT supposed to be entered at the same time. This method assumes you can't trust yourself yet to nail the timing (since you haven't taught it to your hands yet) so you're just trying to see if you can get lucky. Once you get lucky, you can start dissecting what really happened. Did you put more emphasis on your C-stick down input or Z-button input? Did you press UP on the CONTROL stick just a half second later than the C-stick down? Did you kind of flick the c-stick or slam it? Did you go straight from RIGHT to UP on the CONTROL stick or did you kind of roll the controller inputs in that direction Street Fighter style? True, this isn't the most scientific method, but this was what I finally humbled myself to do after the first hour and it slowly (verrrrry slowly) worked. Remember: this technique isn't really taxing on your brain, but very taxing on your fingers. This method will teach the technique to your hands, even if your brain can't fully understand what your hands begin to discover. Hahaha. I can't think of a better way to explain this. Try it!
The Hardest, Correct Way (The most reliable):
NOTE: You already know how to do this. You've seen the video. You've read how it's performed. You just haven't been able to actually DO what you're being told to do. Your brain learned it but your fingers haven't. The following method is my brain's best attempt to rationalize what my hands and fingers are really doing. Interestingly, I find I can do this move just as easily while either running or standing still at the beginning.
Let's assume you're standing still and are doing the dash/cancel/smash to the right still.
The inputs will be only fractions of seconds apart, so to the average person it will look and sound like they're all performed at the same instant. The actual sequence is this:
Forward on CONTROL STICK, C-stick Down, UP on CONTROL STICK , Z attack
Because these inputs are entered so fast, by the time I'm pressing Forward, I'm already moving the C-stick towards down (a fraction of a second away from registering it). Because I'm so stretched for time, I'm ROLLING the Control Stick from Forward to UP, hitting every direction in between EXACTLY like a Street Fighter fireball. In the instant I'm doing this and it's rolling to UP, the C-stick down is being registered. As the CONTROL stick gets to almost 90 degrees (a split second after C-down), I'm pressing and holding Z (like I said, practice with holding Z since it's easier) so it registers at the same time the UP-Input comes in. If I was mid-run when I decided to do this move the inputs are the exact same except I'm holding Forward on the CONTROL stick longer before rolling it to UP.
The inputs have to be so fast that it looks, sounds, and feels like the buttons are all being pressed at the same time. Because the timing is so sensitive and windows are so miniscule, I would NOT be trying to use Sheik's movements as a guide when trying this since you will only go batty. I only watched Sheik to see if she did the move after every attempt.
The gist of this method is simple. Consider a keyboard with your fingers on the "A", "S", "D", "F" keys. Imagine that, starting from left to right, you roll your fingers from one to the next in such a way that each letter appears on-screen almost instantaneously after the next. That's what I mean by rolling. I sincerely believe the ONLY thing that makes this so ****ed tricky with Sheik is the C-stick: it's hard to determine at first just when that C-stick is really registering the down smash for the dash attack. My advice to you is this: Flick or Smash that C-stick. When I'm gentle with it I can never land the move.
If you're having trouble doing it this correct way, try pressing C-stick down the instant you press Forward then just UP-Smash right after that with Z. OR try pressing the C-stick down the instant you press the Z and UP and you might do it correctly that way. Both of these methods are technically incorrect but, as I've stated many times before, the timing is so tight that what seems instantaneous to you is not instantaneous to a computer system. If you can do the move the wrong way you're a step closer than someone who cannot do the move the right way. Just like a maze folks. Start at the end and work backwards if you get stuck
I wish I had more help to give you guys or could upload a video of me consistently doing it to show you the timing (I don't even think that would help so much since it's so ****ed fast).
This took me 2 hours to be able to land consistently. Several days and I'm ALMOST never messing it up (in the heat of battle it's hard to reach that Korean-fingered zen and get the timing on this move every time).
It's a hard move guys. I hope you don't wind up with callouses on your Z finger and CONTROL stick thumbs like I did. Just remember: this move is no walk in the park, so don't get frustrated if it takes you a long time to figure it out.
I've been playing fighting games since SFII, I have long and quick fingers (I type 140wpm), and I'm double-jointed in several places. It still took me 2 hours.
Good luck *salute*