-You may be correct, but the the timing may also just be very tight and I cannot get it. Most meteors flinch grounded opponent's at 0 I can do GnW's dair to grab at 0 and it works.
-I have tried to mash out dsmash while CCing as characters such as Peach, Samus, Zelda. It does not come out in time. I assure you that I will tech in place and I get pulled back into the SideB, this is a common phenomenon as every character I play as. It is possible to get the CC long enough to get shield up, but I'm not sure what allows it or when that is possible.
-Up air KOs GnW at 90% out of upthrow with DI, it may have been the stages we happen to play on, but I've been dying in this range my entire life against Sonic. Zelda escapes upthrow combos though being floaty enough.
-Sonic has tons of options to escape juggles. That is objectively fact.
-I never said I was living to 200%, just that he has conversions at these percents where a lot of characters experience the Marth % where they need a stray hit to KO.
-Aerials are not always fast enough to hit his DownB and he can react to your aerials with counter aerials. Going into the air against Sonic is a terrible idea because you've now committed to something that he can react to and punish. The best thing you can do is throw out sex kicks and hope he runs into them.
-GnW cannot punish DownB in any facet. WD oos > run > dtilt is far too slow to hit anything sonic does out of DownB. Stage control doesn't apply to Sonic because he has the ability to escape all disadvantageous positioning. You cannot corner him unless you have 3 projectiles on a small stage.
You say DownB is a crossup move. So is nair and Somersault. Just because a move can be used for a crossup doesn't mean it should be safe, you use crossups to avoid grabs and attacks from the front-facing direction typically, but that doesn't mean they need to be safe from all angles. A move should be punishable if it is expected, but the only way to punish spins is to be on top of him while initiating DownB, or throw your sex kicks at him and hope they hit.
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Life
The problem isn't him, it's the character. He chooses to play super aggro, when Sonic can play incredibly campy/defensive and it enables extremely gross gameplay. A character like Sonic makes timeouts seem feasible.