Not even a couple of minutes in and this is what happens...
...
*Ahem*.
Cool, it's about time too, I wanted to go over this for a while, to see out there who thinks how we got 6:4 in the first place, because if we're going to do something we get it right or we don't do it at all.
So yeah I think it's an even matchup.
Discuss.
Okay here we go.
Yoshi either has the most aerial acceleration in the game or the best aerial top spee, I'm not exactly sure which is it but I know it's one of them, and regardless of which Yoshi is still quite the speed-demon in the air. However from what I see a lot more of his tricks are on foot. What with the Grab-release shenanigans and all that jazz.
Let's start with basics, since I doubt anybody knows both Yoshi and Sonic extensively (they're both quite the technical characters):
YAY Physics! So this is how it goes down, Yoshi has a tether-like grab; Punishable if whiffed, if otherwise this is how it goes down. Since I hear some stuff about grab-release and all that shizz, the formula to break free via air or ground depends on whether the character grabbed (in this case Sonic) touches the ground with his feet or not. Since Yoshi technically swallows opponents whole, you can only air-break when being released because you're inside Yoshi and of course there's no way your feet can possible be touching the ground in that case. However you can still break free via ground-release if you happen to break free and Yoshi is pummeling (or rather chewing on you I think).
Now I'm not aware of anything Yoshi can do to Sonic after any grab-break, but there are 3 reasons for that.
1. I don't play nor pay attention to what Yoshi does.
2. I have very little actual matchup experience (yes, I'm using theorycraft here, deal with it).
3. If I did have that shizz happen to me, I just react like I'm in a seizure and see if anything works... mainly my first thought of action is use to Spring so I cannot get followed up with anything.
Next, Yoshi's pivot-grab is a little bit more unpinishable than his normal grab... better get used to it since we're assuming here your opponent can use Yoshi at the top of his meta-game, meaning they can do stuff like Draconic Reverse/retreating grabs to speed up his grab and act much faster.
Grab-releases out of the way, let's look at what else is in store.
Yoshi's Nair acts like a C-C-C-Combo breaker, but I suppose you need not to worry about it if you space your aerials right... probably easier said than done, remember Yoshi is quite the aerobic creature.
Bair is quite disjointed and lasts for a while... can be ACed IIRC.
Then we have Uair... it kills...
You shouldn't worry about his Dair/Fair since they have considerable lag/are easily read, outspaced and outsped by Uair/Bair. I suggest you not try to pursuit Yoshi in the air any further than SH height, just spam SH Uairs.
Okay, specials!
Egg Toss... it will probably force you to approach Yoshi, but it's not so bad since Sonic can just put up his shield from running... in fact you're so fast you shouldn't really have to worry about this too much, just know that Yoshi can throw his Eggs wherever he feels like, so don't end up running right into them whe you tried to avoid them... -_-
How often would you get caught in Yoshi's Neutral-B and transformed into an egg... really...? All I know is that if Yoshi can read you out of breaking out of the shell, you can die... or you can get damage racked up on you depending on how long you are encased in the egg.
Yoshi Bomb is defenitely something to look out for... it works like the Bowser bomb that if done from the ground you will be put right into the path of the next part which is considerably strong. It has some after lag, but usually his sides will be defended, so you will have to punish him from the air. Don't get predictable in your approaches.
Egg roll... hrm... it's lulzy, but I think it works like Sonic's SDR where it will either get beat out with enough priority, or it will knock you out of some stuff, or clank. If you try to beat it with SDR, the result is luckily you will get hit out of it since he will have his fresh (if he even bothers to use it).
Then we have standard attacks.
His UTilt works like Sonic's... I think... just how vertically disjointed is it?
FTilt can go a little ways, it'll probably push you away if he times it right, or clanks if you were SDRing at him... Not too much window of opportunity for him to mistime it and suffer dead-frames AFAIK. Jab does the same thing as his FTilt, but it being so fast it will clank and then just hit you out.
Fighting Yoshi is like fighting R.O.B., just get close enough where you can't be punished, but if he does anything you will have enough time to punish if you're on your toes. Yoshi's shield is not exactly the best, sure you can't shieldpoke it, but IIRC he cannot react OoS like say Marth can or something. I wonder if he has a different timing for PSing too, if they want to be that crucial in shaving off shield lag...
You won't be gimping Yoshi BTW, he can just airdodge through most if not all of his 2nd jump, so just read his recovery path and wait for him to punish there.
Go for "flat" stages, so that you can find ways around Yoshi and attack.
That's all I can come up with... for now.
I like to Egg Roll in this matchup because it makes me feel like I'm a blue hedgehog, LOL!
I like to Volt Tackle in this matchup because it makes me feel like I'm a blue hedgehog, LOL!