Ive been playing against a pretty good corrin player lately, and I think the Mu is pretty much a 50:50 or 55:45 in Fox's favor. In the neutral we can beat him out pretty well, and he's not too hard to combo, you just HAVE to know when to stop pressuring and reset to neutral. Also his neutral B isn't a threat due to shine. (I reflected a shot which hit him and had enough time to run across the stage and Usmash Corrin while still in stun). However offstage can be very scary due to counter, nair, and dair if you're down a stock. Also be careful when at high percents and going for uair, if countered you can die VERY early. With that said, baiting out counters can be extremely beneficial as it has a ton of CD. Lastly, from what I've noticed, Corrin's side B, when impaled in the ground isn't toally disjointed so you can hit the lance (or whatever you wanna call it) with a dair and tack on some extra damage. Make sure to space well against corrin, you will have a very bad time if you don't.