I'm bored so I'm actually gonna write up my sheik ditto strategy for you
Okay, Sheik dittos are EASY as ****. You need to do a couple of things beyond all else:
1. Stay on the ground. STAY ON THE GROUND. That means stay away from platforms, too, unless you know you'll get on the ground before them. Whenever a Sheik is above me, I just wait for them to land (or try to land) and fair / utilt / dtilt / dash attack them.
2. Crouch cancel everything. Almost all the time you get hit you can CC into a dtilt. Dtilt is probably Sheik's best move, you need to spam the **** out of it. When you fair a shield, go into a dtilt because they can't shield grab it. BUT YOU MUST SPACE OR I CAN SHIELD YOUR DTILT AND GRAB YOU OUT OF IT!!
3. Spacing. Spacing. Is. Everything. If you don't space, you get grabbed. If you get grabbed, you die. You see, if you space filts into the shield, they can't do anything. If they try to attack you or shield grab, you can respond before them and they'll just eat another tilt. If they roll, they get dash attacked. If they jump, see No. 1. If they spot dodge, you're spaced and they get grabbed. If they don't space, on the other hand, you can shield grab, wd in and shield if they like to throw out moves and then shield grab, or you can nair out of shield. Nair out of shield is the safest thing Sheik has when you're trapped in shield or anything so keep it in mind.
4. DI away. Away away away away away. Otherwise you just eat more tilts. If I ftilt and you don't DI all the way away, I just walk up to you and ftilt you again and again until you do. If your % is too high for me to follow up when you DO DI away, then I cut it short and fair you. You can also get out of dash attack to fair at higher percents if you DI away and up.
I'll break down the matchup in a couple of aspects:
Edge guarding: Sheik is easy as **** to edge guard. Just grab the edge and space bairs or throw needles to make sure Sheik HAS to up b on the stage. After that you can grab, bthrow, throw out the bairs again (but you have to know when the recovering Sheik has spaced herself so you don't just throw it out for no reason, a problem mediocre players have). Or if it's at lower percentages, just grab and CG / dthrow combo.
Grabs: A lot of Sheiks don't combo properly, but Sheik combos the **** out of Sheik. The first thing you want to look for out of the grab is making sure they DIed away. If they didn't, utilt or ftilt **** them. You can't ftilt to fair at lower percents so don't do it, either fair or dsmash. But the gold mine is landing the dash attack out of the dthrow. That is the second thing you should be looking for -- at lower percents if they DI away, dash attack, then you can utilt / ftilt or just fair (at edgeguarding %s).
Low percents: Low percents are the hardest to deal with because Sheik's CC is broken. If you do a dash attack or a dsmash it will be CCed and you will be grabbed or dtilted back and it will hurt. Do not allow this to happen! How? YOU MUST SPACE! Spacing is by far the most important at this juncture (though it's always important). Bairs are my favorite. You can also get away with dsmashes but only if it's perfectly spaced. IME you can get away with spaced dsmashes about 20% and up, but it's still not advisable because you can still get punished out of it and, more importantly, because every time you do a dsmash you had a better option.
Dash attacks kind of work at lowish percents, but you have to make sure you finish the move behind them. I'm pretty sure if you do you have time to buffer a spot dodge if they CC and come after you (watch Drephen vids for more). But it's not advisable if you don't know what you are doing.
Approach: Approaching Sheik is hard because of the CC and gay tilts. This is why I prefer CGs because you are only looking for one grab to end the stock. If you agree to no CGs you have to switch it up a LOT because any one approach you do can get countered and punished really quickly. I have a couple of bread and butter approachs, though:
- Empty short hops. I like using these at low percents because if I space it eliminates their CC, and a lot of (bad) Sheiks like to throw out cc dtilts / dsmash whether you space or not. If you don't space, you get ***** by noob ****, but if you do you can just jump right after and fair them again. Anyway, empty short hop is amazing because it's really versatile. You can reverse needle cancel to a bair, you can feint needles and fair, you can wd back and ftilt if they threw a move out, you can wd back and dash attack, you can wd in place or wd back to space yourself, etc. Be creative.
- Stay on the ground and just walk to your opponent. Here you're just reacting to your opponent, but you have to be careful not to throw out moves or they'll bait it and you'll get *****. Try to push them to the side of the stage where they have to shield, jump, roll, or get the stage. If they refuse to approach you just start camping and throw needles. Remember, all you need is that first 30% or so and you can start comboing like normal, you just have to play REALLY REALLY carefully until you get it. Every percent matters.
- Platform / needle camp. You basically sit right under a platform and make them come to you. Camp needles and bair. Nair out of shield. If they commit themselves to you, you can jump on the platform above you and run away and protect yourself with a bair / isai dropped bair.
I'm a really campy Sheik so a lot of my strategy revolves around camping them and making them do the first move. All you need is one opening and you can literally combo Sheik for the whole stock, so be patient and space. Patience, spacing, and CC. That's the whole matchup.
EDIT: Oh yeah, it goes without saying that the first thing you are looking for in any situation is a grab. If you know they always come down with an aerial before they land, then time a boost grab or jump cancel grab, not a dash attack. If you know the timing of your option is going to succeed, you want the grab first, no matter the percentage.