Edit: weighing on Sonic. This match up plays heavily on bait and punish, well that seems to be a whole lot of what Sonic does. Sonic likes breathing room, so if you can do your best to stay between tipper range and 2-21/2 sword lenghts away from sonic, Anything larger or smaller than that is effectively making sonic comfortable. if sonic starts charging spin dash... Breathe, its ok he isnt hitting you yet. WALK to sonic, WATCH sonic, when he takes off you have a few options, shield, counter, roll forward. spot dodge, or try to space the ball. I'm niot a huge fan of back roll. Ok so the most favored option by sonic (from my experience) is he likes to dash into you then go through you with a fair or an up air, if he end up behind you (you better have tap jump on) jump cancel your shield to up air, more often than not it will tip him if you time correctly. If sonic mistimes it bad you can actually up smash him, so watch for mistakes.
If sonic spins past you hold shield then chase the follow through, go for any aerial option as all of ours beat his pretty much, sonic is pretty much meat in the air and well he spends quite a bit of time in it. the goal is to hit him, not knock him out of the park, and at any point in the match up just aim for hits, you'll eventually kill him with bair or up throw, if you see an obvious smash puniish go for it. Patience is the name of the game in this match up.
If sonic just sits there and spins, continue walking to tipper distance and throw out something like dtilt, jab, dancing blade.
Once you are at higher percents sonic takes on a different behavior, he'll start camping you at the ledge of the stage, it's pretty obviious what he want, and that's a bthrow, don't get baited into getting grabbed and play ultra super safe and space well, you can give him a really big headache with grab attempts sometimes. Sonic should not be killing marth with anything but up smash, and fthrow.bthrow otherwise you misapced or messed up something. the up smash is from grabs too, and reads on landing.
50/50
Folks, I play a lot of wifi in order to practice for my in persons (doing one every week of April, will be my first time truly active since 2009) And one match up stands far and above as harder than others to me and that's bowser jr... of all things right? I can't seem to space him, and hes almost like playing with a sonic, well except he has explosives crawling on the ground that I must be aware of during his approaches. Makes things a giant headache, the match up feels like a knowledge deficiency on my part, and well the bowser jr boards don't really seem to help.. Care to discuss Bowser jr.? I'll add what I have to say after I get confirmation.