I haven't really been active here, and I don't feel like posting anyway. So I'll leave you with this. It's a collection of my personal experience and the advice given to me by none other than Super Moderator Amazing RyokoYaksa.
Forward Tilt
Sheik's forward tilt is, overall, the best move she's got. It's the second fastest attack (slower than jab by two frames), and it's got weak damage (5% undecayed) and knockback (KO at around 300%), but that's not what makes it so amazing.
Well, ok, the speed and knockback have a hand in it. Sheik's forward tilt hits on frame 4. It's got good reach. This makes it a very effective tool for out-of-shield punishment, trumping the grab in reach and overall usefulness and the jab in area of range. And its knockback is so weak that at low-to-mid %, the opponent barely goes anywhere.
This leads into setups for true combos, which are quite rare in Brawl. Most notably, the ftilt lock, which is equivalent to a chaingrab for 30-40% damage with a practically guaranteed ender.
Ftilt Lock
This is the defining "broken" ability of Sheik. Use it. It will take out half a stock, or even a full stock. It destroys lives. It ravages souls. It leads into Sheik's strongest finisher.
Controversies
But it's cheap!
Get out of my thread.
But, Gimpyfish doesn't use it!
Gimpyfish is one person. He also is not particularly concerned with winning for the sake of winning in a friendly game. Forgoing your single best option in favor of "style points" in a tournament match is not recommended.
Usage
The ftilt lock has a couple of characteristics that are important to keep in mind for keeping things effective. First of all, make sure not to use it before 30%. Second of all, don't end with usmash unless you intend to KO with it or Transform.
Options
Away DI
This is actually the wrong direction to DI. Continue ftilting.
Towards DI
DIing in this direction will pull the character into and behind Sheik.
Reverse Ftilt
If you can see the moment the character moves to the other side of you, this is the best option. It will continue the ftilt lock.
Utilt
This ends the ftilt lock with upwards-away knockback and 13% damage. It's pretty much the standard ftilt lock ender.
Dsmash
If you can't consistently reverse ftilt, this deals 13% and has a more favorable knockback power and direction than the utilt.
Down DI
The logic here is to use any possible moment of non-hitstun to fastfall into the ground and powershield the next ftilt. To avoid giving this option to the opponent, make sure not to ftilt before 30%.
Grab
This is the only thing that gets past a shield.
Dsmash
If you notice that you're at too low of a % before the opponent does, this is your quickest option to avoid repercussion for your mistake.
Up-Away DI
DIing up and away will make the ftilt connect later and possibly allow the opponent to jump out. It stilll keeps them in hitstun, though, so if you can see them about to escape then just lead into an ender.
Nair
Serves about the same use as utilt, except that if they DI only upward, this has more chance of hitting.
Utilt
The standard ender.
Fair
Weak and low-angled knockback. If caught off-guard, this can be used to lead into another ftilt lock setup.
Uair
Harder to hit with, but with straight upward knockback this can give Sheik a better juggling opportunity.
Up/Up-Towards DI
I'm not entirely sure why people choose this direction, as it gives Sheik the greatest number of ender options.
Utilt
Of course.
Nair
Also good.
Uair
Yep.
Usmash
The scariest ender yet. Since ftilt will lead into a tipper hit, this will deal 17% damage and have a very strong upward knockback. However, this is also Sheik's strongest KO move, so don't bother ending with this unless at a % that usmash would KO, or going Zelda would KO.
Dsmash
If they're moving more towards than up, this will cover the most area and thus have the greatest margin of error.
Bair
You could do this if you're standing at a ledge but facing away, I guess.
Ftilt Usmash KO
This may sound impossible, but thanks to the miracles of attack decay, this can happen to any character, from Snake to Jigglypuff. Use your ftilt lock and continue to keep it decayed with liberal usage of small ftilt combos like ftilt nair and ftilt utilt. Eventually they'll reach the right % to die from an usmash and you can go ahead and set it up.
If you got them up to over 70% and then they KO'd you, resetting your attack decay, it might not be worth bothering with this setup, but you can still use ftilt to set up into aerials.
Forward Tilt
Sheik's forward tilt is, overall, the best move she's got. It's the second fastest attack (slower than jab by two frames), and it's got weak damage (5% undecayed) and knockback (KO at around 300%), but that's not what makes it so amazing.
Well, ok, the speed and knockback have a hand in it. Sheik's forward tilt hits on frame 4. It's got good reach. This makes it a very effective tool for out-of-shield punishment, trumping the grab in reach and overall usefulness and the jab in area of range. And its knockback is so weak that at low-to-mid %, the opponent barely goes anywhere.
This leads into setups for true combos, which are quite rare in Brawl. Most notably, the ftilt lock, which is equivalent to a chaingrab for 30-40% damage with a practically guaranteed ender.
Ftilt Lock
This is the defining "broken" ability of Sheik. Use it. It will take out half a stock, or even a full stock. It destroys lives. It ravages souls. It leads into Sheik's strongest finisher.
Controversies
But it's cheap!
Get out of my thread.
But, Gimpyfish doesn't use it!
Gimpyfish is one person. He also is not particularly concerned with winning for the sake of winning in a friendly game. Forgoing your single best option in favor of "style points" in a tournament match is not recommended.
Usage
The ftilt lock has a couple of characteristics that are important to keep in mind for keeping things effective. First of all, make sure not to use it before 30%. Second of all, don't end with usmash unless you intend to KO with it or Transform.
Options
Away DI
This is actually the wrong direction to DI. Continue ftilting.
Towards DI
DIing in this direction will pull the character into and behind Sheik.
Reverse Ftilt
If you can see the moment the character moves to the other side of you, this is the best option. It will continue the ftilt lock.
Utilt
This ends the ftilt lock with upwards-away knockback and 13% damage. It's pretty much the standard ftilt lock ender.
Dsmash
If you can't consistently reverse ftilt, this deals 13% and has a more favorable knockback power and direction than the utilt.
Down DI
The logic here is to use any possible moment of non-hitstun to fastfall into the ground and powershield the next ftilt. To avoid giving this option to the opponent, make sure not to ftilt before 30%.
Grab
This is the only thing that gets past a shield.
Dsmash
If you notice that you're at too low of a % before the opponent does, this is your quickest option to avoid repercussion for your mistake.
Up-Away DI
DIing up and away will make the ftilt connect later and possibly allow the opponent to jump out. It stilll keeps them in hitstun, though, so if you can see them about to escape then just lead into an ender.
Nair
Serves about the same use as utilt, except that if they DI only upward, this has more chance of hitting.
Utilt
The standard ender.
Fair
Weak and low-angled knockback. If caught off-guard, this can be used to lead into another ftilt lock setup.
Uair
Harder to hit with, but with straight upward knockback this can give Sheik a better juggling opportunity.
Up/Up-Towards DI
I'm not entirely sure why people choose this direction, as it gives Sheik the greatest number of ender options.
Utilt
Of course.
Nair
Also good.
Uair
Yep.
Usmash
The scariest ender yet. Since ftilt will lead into a tipper hit, this will deal 17% damage and have a very strong upward knockback. However, this is also Sheik's strongest KO move, so don't bother ending with this unless at a % that usmash would KO, or going Zelda would KO.
Dsmash
If they're moving more towards than up, this will cover the most area and thus have the greatest margin of error.
Bair
You could do this if you're standing at a ledge but facing away, I guess.
Ftilt Usmash KO
This may sound impossible, but thanks to the miracles of attack decay, this can happen to any character, from Snake to Jigglypuff. Use your ftilt lock and continue to keep it decayed with liberal usage of small ftilt combos like ftilt nair and ftilt utilt. Eventually they'll reach the right % to die from an usmash and you can go ahead and set it up.
If you got them up to over 70% and then they KO'd you, resetting your attack decay, it might not be worth bothering with this setup, but you can still use ftilt to set up into aerials.