Please know that the following is all given with a
very sincere degree of humility, as I am not at all pro at this game or fighting games in general; however, I do feel (again, humbly) that I have enough Yoshi knowledge and experience to give you some
basic advice.
OniNeko, your problem as I see it is
not combo knowledge. I mean, you may not know combos, but that’s not what is killing you. It’s attacking at disadvantage, using to many mids or naked supers without any hope of opening up your opponent, lack of good defense, not using his stances appropriately, etc.
First,
never use Yoshi’s CE as a “my turn” kind of attack with no setup. Everyone and his dog will block it low and stuff it. If you’re facing someone who’s spamming a slow high attack (and why would they?) a random super
might work, but that’s not the way to use it. One very good setup for CE is Yoshi’s 22_88K - this leaves you at ±0, but
everyone seems to think it leaves Yoshi at disadvantage and goes for an attack afterwards. So, a great opportunity to unleash your CE.
Second, Yoshi’s 4K,B is only effective in several situations: 1) when mixed up constantly between that and an effective low, like FC3K,2K; 2) as a wakeup tool, and 3) in wall strings when you want to seize a bit of a risk/reward. It’s also fun as a random tool for applying pressure, but only if you are very clever and lucky with the timing of the release on the (B); not a recommendable strategy.
On the subject of effective lows - use FC3K a lot more. It is almost unreactable, gives you a free 2K afterwards, and against noobs can be spammed a little before they catch on. Even after that, simple mixup between FC3K and 4KB is effective. Another very important low is 214A, which combos into DNK 3B and TCs to boot. Pros will guard it, but most online players will eat it. And of course, 2A and 2K are BnB for interrupts.
Mixups reminds me: any time you knock them down, strongly consider taking advantage of the time it gives you to go into DGF stance. It’s a great stance, people will be terrified if you use it properly. You can go up into SDGF B UB, you can mixup between DGF K DNK 3B and DGF B 3B 6K (or better combos after some practice).
On the defensive, simple tools include 22_88B against verticals, FLE K A+B against lows, 6K as a terrific punisher against anything that’s -15 or worse on block, standard AA or 2A or 2K for interrupting, etc.
Stance games, stop using MED so much as most people have seen it 10,000 times by now and all of the MED options can be defended. Focus on building your FLE, DGF, and SDGF game more. An easy time to enter DGF is after knockdown. An easy way to enter FLE is 2(A+B).
Those are all some basic Yoshi strategies and are by no means comprehensive, nor the
best options, nor specifically what
you need to improve your game. However, I hope that you might find them helpful starting points. Good luck, and keep at it - Yoshi is a very fun character, IMHO. Cheers!
On a side not, [Sieg] doesn't seem that bad to me, people say he's F Tier, yet, with enough potential you can atleast be average with Sieg. :P
SCV is balanced enough that anyone with enough skill/knowledge can beat people with less skill/knowledge with virtually any matchup. It’s only really at higher levels (certainly higher than my level, at least) that Sieg’s low-tier status starts making him actually ineffective. You’ll quickly learn his moves though, he telegraphs a lot and is pretty slow for how much damage he does. He got nerfed pretty significantly partway through development, but I suspect he may be buffed during this upcoming patch. It will be interesting to see what happens as it might indicate to whom Namco is listening the closest: the mainstream online crowd, or top offline players.