Peach and Sonic is an even matchup, sure, but Peach has to stick to her tried and true playstyle with minimal effort to stuff Sonic's bread and butter everything, but Sonic just has the neutral down here and doesn't have to work hard to avoid HER, but the entire battle is a lot more work to get ahead. He has to play by her rules and she dictates the pace of the match, but he has the tools to play by them, but overall it's coming down to stray hits and nothing else.
Snake... the thing is that the nades and mines are more my plaything than Snake's at times. Proper spacing of your aerials(and knowing your angles and speed) really allow you to stop eating 'nades all the time, and while Snake's recovery does limit what you can do, properly spaced Fair still works(and connects with the meteor!), and I like to come at him from below anyway. Once he goes below the stage, just moonwalk, short hop, and wait for the DJ>UpB, position yourself with your own double jump and bair him. Best he can do is nair you at that point, and then you just SDI away and spring to safety. When Mines are down I know which throws will send him where he doesn't want to go, and the influence of a Snake's DI - so it allows for easy reads and followups. If a mine is in my way, I just slide into it from a Dash and WD OoS back out, or wherever I wanna be.
A good mash counteracts a tranq, and if you get stuck, well, usually I don't let it affect me. I know what he wants at that point, so I just poke him where I can and put him off stage. Snake's LOVE to use a sticky to screw up an opponent's edgeguard. If you go off stage, just be on point with waiting for your DI and stagetech and then continue the edgeguard.
I mean, thanks to backthrow, you still can grab Snake for free even when he does pull a 'nade. I'm usually in the air myself and, when looking for tranqs, I like to hop my SideB's around Snake.
Just be patient around Snake. You don't have to go in if you don't want to - if he puts a C4 and a mine and a grenade where you don't like, sit somewhere for a minute if you have to - he's going to have to make a move first. Jump at him without an aerial when he's in the air and bait out the grenade pull and punish what he does afterwards. Snake is a technical and creative character - do the same back at him.