Rawr that's 8 o' clock, but I'll just call it even since a couple of us agree to that, and both saids have people saying it's in X character's advantage.
Uhm... moving on, let's talk about Ivysaur now.
I think Ivysaur is an Olimar without the Pikmin requirement.
It has no reliable third jump, poor aerial mobiltiy (I think Ivysaur has the third worst mobility in the game if I read/remember that somewhere correctly), still doesn't mean they can't just Razor Leaf you if you try to hang on the ledge to knock you out and snap onto it themselves, so beware of that if you try to edgehog Ivysaur.
Razor Lead while on the stage... is very slow... slow enough where I think you could do a Spinshot into a Boxobair over any Razor Leaf, no matter the angle.
Sonic isn't as suspectible to Bullet Seed as some other characters are. Sonic is skinny and about as tall as Mario... with pretty good aerial speed to escape Bullet Seed. I suggest you stay in the air so that if Ivysaur misses it, you have about a full second to punish it, because it takes some time to drop BS, and besides that the initial hitbox that sucks you into the BS is on the ground, so if you're in the air, you won't get pushed into the ****. Being in the air probably also allows you to take less damage from BS if you're far on the side.
Now that I think about it, just how well can Sonic punish BS after he gets out of it, can't he just Dair/ FF Bair after he breaks free from the BS to hit Ivysaur before it drops the move?
Moving away from special abilities now... Ivysaur has a Bair that has long range,, and Sonic has nothing in his moveset to answer it with, so anybody got any suggestions to move around that?
Fair has some decent power, but a bit of lag, and as we all know, Sonic is pretty good in that field.
Nair can probably be SDIed up and away from Ivysaur, just Spring if you get caught in this. Now as for punishing it, a simple Bair/Dair should take care of it.
Then there is Uair and Dair, very powerful, let's Ivysaur stall in the air for a bit, or gets him down a bit faster. Ivysaur really only has one shot to hit you with Uair, just avoid that anyway you can. Treat it like you were your opponent trying to avoid Sonic's Spring to Uair K.O., he can only hunt you down for so long before he can't chase you because he has to freefall to get footing again.
I'll say more once we get a couple more people participating here.