In this MU the goal for both characters is to remain patient in neutral whilst capitalising as much as possible in advantage.
A good tool for Sheik in this MU is Needles. They keep Sonic more honest in neutral, as they are difficult to react to forcing pre-emptive shields, which the Sheik can capitalise on allowing her to control the game at her own pace. Fortunately, Sonic is one of the better characters equipped to get around them. Because of their range nerf, the Sheik's spacing with them has to be quite tight to make them safe against Sonic, as the move has quite a bit of lag which Sonic can easily punish if they're used carelessly. Therefore, applying pressure and holding stage control against Sheik is very important as to make them second guess themselves with their projectile play.
The best spacing for Sonic in this MU is close enough to pressure Sheik into not throwing Needles whilst also staying out of her immediate burst range. Once you have this spacing you can begin mixing up with spins. Sheik has better buttons than Sonic which can lead into combos, similarly to Ryu, so try to stay away from QCQ and focus on counter poking with moves with decent range (ftilt,bair) or shield grabbing poorly spaced attacks.
Both characters can exploit each others disadvantage. Edgeguarding is unlikely to happen because both characters have difficult recoveries to mess with. Although risky, it is possible to hit Sheik's Vanish before its intangibility starts, as it only kicks in after 19 frames, but this should be rarely attempted. Getting off the ledge against Sheik is tough however, largely because of her nair having a big hitbox, lasting a while and being able to combo into a Bouncing Fish. Always be aware that the Sheik is possibly conditioning your ledge options. On the other hand we have stronger juggling than Sheik does, so be sure to capitalise on her landing, be aware they may mix up with Bouncing Fish.
Kill power in this MU is interesting. Sheik's throws have been nerfed in terms of being able to set up KOs, if you DI away and jump you can escape most of them. The only thing to be aware of is DI mixups with bthrow, which can lead into a fair or BF for the kill, pay attention to their positioning so you can guess when they'll use it. Post patch Sheiks will be more inclined to use ftilt and tipper dtilt to set up an uair for the KO, or will try to read your reaction. Jumping away will again help to avoid most of the set ups, but be sure to mix up. Sheik in general lacks lag, so landing a slow finishing move can be difficult. Having kill throws is really useful, since Sheik's weight in addition to her struggles killing can result in rage throws killing very early, the earliest I've seen be 117% on FD to an uthrow.
The best stage to take Sheik to is Lylat Cruise, because the tilting hinders needle play. Duck Hunt is also a good stage because Sheik can't pressure Sonic in the tree very well. Final Destination and Smashville should be avoided, since the lack of platforms makes needles stronger whilst Smashville's platform helps extend Sheik's combos.
General stuff on Sheik:
- They can cancel the end lag of Grenade by grabbing the ledge.
- Bouncing Fish can bounce off of surfaces and present a second hitbox, be aware of it.
- Spinstool dair works on Sheik and doesn't have to be buffered.
- When Vanish is used from above the ledge, it ignores the 2 frames of ledge vulnerability.
- When under platforms stay aware of tipper Usmash, it is Sheik's strongest kill move capable of killing at 70 with rage.
Overall both characters are well equipped to deal with each other's kit, also worth noting is that both characters benefit heavily from a lead. The players of each character are pushed to their limits at high levels of play.
50-50