I don't think Pyrrha is that bad for Yoshi. Just turtle her. She gets away for free, so let her. By turtling you can win against both aggression and turtle vs. turtle. By turtling I mean play the neutral game with iFC 3K and dash iMCF, and if you knock her down just 1B+K and back off. Even 2K is risky against her, so just throw her or do more iFC 3Ks.
Worst
1. Natsu - Her evasion is safe and also catches movement, so you can't bait evades. Of 8KA, A+B, 66B, and 22A, three of those beat iMCF, two of those beat iFC 3K. 8KA evades everything in a huge window is very difficult to stop even if you know it's coming. 66B will evade 2B, BB, 6B, pretty much all your sensible mids except 3K, which is beaten by 8KA. 8KA is unsafe but they can buffer the A late, so they can wait and see if they evaded something. Delayed attacks don't help much at all, with the speed and long and late evading windows. I feel pretty much forced to play a losing neutral game with the usual 2B, 3K, and iFC 3K due to her evades. Actually, you can't even really discourage her evades by playing a neutral game because her neutral game is basically 66B and A+B, which are evades and are tricky to whiff punish. Oh yeah and don't forget she easily punishes your -12s. The only thing I feel successful doing in the matchup is desperately spamming iFC 3K and throws and starting his oki vortex, throwing in wild 6Ks (confirm for the second K) to stop jumping (does 100 damage with this read).
2. Aeon - He can try 66As pretty much for free with good spacing, and even if you somehow backstep it, it is impossible to whiff punish it. You can only hope to block it up close and run in, but again, you can't whiff punish it, so why would they miss-space it, they don't even have to worry about not being close enough. Say you do block a mid-spaced 66A, 4B+K, or tip 3B. Aeon still has a mixup against you. 4K just barely won't reach, so now you have to move and squander your +frames. Well, most of your +frames. Turns out that dashing in and iMCFing is Yoshi's fastest ranged move, and with the amount of +frames that you get for blocking those, you can interrupt stuff like Aeon 66A 2A, but with great difficulty and spacing dependence. However, Aeon can start backstepping and sidestepping and be pretty much home free. Your counter to this is mixing him up, while still beating move-attack. That leaves you with dash-in iFC3K and 4KB but those still won't quite beat all timing variations of move-attack. Don't dash-in enough and you might just whiff. Dash too far and he'll be able to interrupt you even if he moves and attacks. Basically, you have to vary your dash-in attack timings of dash-in iFC 3K, 4KB, and iMCF, mixing in some patient dash-in steps or dash-in (just) guards, throws. Unfortunately, that mixup is trash against Aeon. Aeon gets his WR B launch for blocking iFC 3K, launch punishes 4KB on JG, and backstep-3B is safe enough throw out to whiff punish iMCF. Risk-reward just isn't in your favor, and it's either do this or play a losing neutral game.
3. Viola - She punishes iFC 3K with 44A and has too many +frames in her pressure for Yoshi's speed to mean much. He has no great tools to deal with her pressure, even GI isn't that great compared to some other characters.
Best
1. Maxi
2. Ezio
3. Pyrrha (compared to her other matchups)
