From what I understand on this matchup, these are the things sonics can do in this matchup.
1: don't get grabbed. actually, this isn't hard for sonic, but one grab into dthrow completely shuts down sonics momentum and is put into a guessing game. his forward and back throws set up mortar slide setups as well, and if you are off stage, he's going to try for a grab setup or f tilt.
2: grenades are not the key for snake against sonic under most circumstances. sonics's generally small hitboxes help in this matchup against grenade counters, which happen when a snake holds a grenade as you attack, in hopes you will blow it up and not only reset advantage or flow, but because snake is a tank, and you are not, its fine as long because one uptilt at 100% ends you usually. you can abuse spins and jump cancel out of the attack before you come in contact with the grenade. also because of sonic's glide toss, he can utilize them just as well as snake and can work on setups so long as the sonic isn't scared of them blowing up. back throw negates the threat of grenade counters completely AND sets up snake for juggling/edgegaurding.
3: up throw is key, because its you best throw damage wise, and revels snakes weakness from below him, his most common defence is airdodge, or di away for bair, both extremely punishable by sonic. upair ***** characters with slow dairs, and since its disjointed, most of thte time you will win and juggle him. juggle , bait the airdodge, with an empty jump, then upair again. this also helps your tilt game beacuse you can bait and punish him into tilts that lead into more juggling.
4: snakes CQC is very good. Ftilt if both hits connect leaves him open to grabs and IDA. but most good snakes mix the first hit of ftilt and jabs, to trick you, and eventually go for grabs.
just get the dude in the air, you have the advantage. patience will help in this match when you are fishing for juggles. i've used YI:B with ISDR to negate the explosives even furthur, and i like stages that give me lots of room to run so i can choose when to attack, since snake cant really chase me. you will lose if you run into ftilts often. if i need to i will continuously move around so that he cant' pin me with nades as well, and quick sudden movements like foxtrots bait tilts and jabs.even though you can run all over him and negate those grenades to an extent, his attacks are too strong and he'll even it up easily. i honestly think its more of an even matchup though.