My nooby two cents on each of the matchups.
Fox 55 - He's faster and more mobile, but like many of Fox's other matchups, you can force him to approach, and punish his approach. You have a large arsenal to beat his *** with once you have him in a combo, and you can also edge guard him decently. That said, usmash and uair tip it in Fox's favor, imo.
Falco 50 - I accept the fact that I am horrible at this matchup, but I believe that it's even. As long as you can break Falco's cool exterior and make him commit to a move, that's your make or break moment. If you manage to hit him, he should die. If he manages to hit you, you should die. It's quite cutthroat, imo.
Puff 55 - I don't really have too much of a problem, but then again, the level of Puff I've played is only so high. Biggest thing is to watch your dash attack, smash attacks, and grab. Best to rely on ftilt, utilt, and while in the air, focus on safe moves to outprioritize, like uair, and bair. Nair only for combos because Jiggs can beat it with everything, pretty much. Also, missiles. Lots of them. She can aerial through them, but if you have a location where you can shoot double the missiles, i.e. platform cancel them, throw lots of homing at her. The fact that she can edgeguard you pretty well makes this 55 in Jigg's favor for me.
Sheik 60 - She has an answer for just about everything Samus can do. However, as long as Samus can bait her into using something, there are followups and punishments. Also, edgeguarding her isn't hard. Whenever I play this matchup against good Sheiks, I feel like it isn't Sheik beating me, it's them. As long as you can space well, you can definitely make the matchup hard.
Marth 70 - Unlike Sheik, Marth has an almost universal answer to Samus's whole movelist(spaced fair), and it is nearly unpunishable. It may be my own mentality limiting myself, but I've played lots of Marth Samus, and it really feels horribly lopsided to me. The only time Samus has any fighting chance is to get down to the bottom floor on stage with platforms, and with Marth, that's really not easy. Once you're on the bottom floor, I think one of your only decent approaches is to dash mindgame for dash attack or grab.
Peach 45 - I feel like Samus has an answer for anything Peach has, but Peach has more mobility and upward killing power, while you're forced to kill Peach off the sides. Both're about equally hard/easy to edgeguard, imo. On the ground, your tilts outrange her. In the air, most of your aerials beat anything she has. The only chance she has is to turnip approach, and you can beat that with missiles. I feel like it's in Samus's favor, definitely. Charge shot just seals the deal for me.
Falcon 50 - This is Darrell's opinion, really, but it's one of his that I've come to agree with. Falcon should never hit Samus. If Falcon has attacked and not hit anything but shield, Samus has messed up. As long as you can predict an approach from Falcon, CC dtilt is situationally nice, wavedash back dtilt/dsmash is probably better. If Falcon's in his shield, Samus's shield pressure is good enough to force a hit, I think. Off the edge, Falcon should never live, and Samus should rarely die. Keep your jumps! Falcon's long jump knee to double jump uair shouldn't hit you as long as you keep your jump. You can always back out of his range, or use a bomb jump to dair him if you can predict his timing and trajectory. If you don't sweetspot the stage with grapple, you can wall jump air dodge onto the stage for more recovery mindgames. All in all, I think that while Falcon has the edge on the stage, it's not overwhelming, and Samus has the edge off the stage. Feels even to me.
Ice Climbers 40 - Utilt. Ftilt. Dtilt. Space your tilts, **** up Nana. Space your tilts, **** up Nana. I personally also use Dsmash, but really, I just need to space moves such that when they impact on IC's bad shield, I won't get grabbed. Your aerials are better, and missiles are great if you can space them over the glaciers at the ICs' heads. I haven't lost to an IC in tournament yet after playing 3 or so, but I guess I've yet to play any notable ones. The matchup feels like Samus's favor though.
Samus 50 - I dunno, guys... I dunno.
Ganon 60 - I don't have much experience, but really, it feels like ****. I'll get back to you guys with a more educated understanding.
Doc Mario 60 - ohgodthefistitscomingandicantdoanythingaboutit I've only played three Docs. Bob Money, Shroomed, and Home Made Waffles. I think I'm allowed to have an unnatural fear of Docs. Again, when I play the matchup more and understand it better, I'll probably change the number.
DK 45 - The little DK I've played has told me that as long as he isn't bairing you, you should have the advantage here. Other than that, I think Mexican beat me because he's a better player than I am, not because of DK.
Link 60 - This is actually my favorite matchup. I can play this for days on end and not get tired of it. That said, Link has lots of answers to Samus, and projectiles to boot. It's about finding your way past the storm of objects, avoiding and beating his aerials, forcing him into his shield, avoiding his two out of shield options, and then ****** him. To me, it feels like playing chess, with all the options both players have. It's so complex and deep that I don't think we have the right answer to it yet, but since Link has the options on his side, I'm going to call it in Link's favor.
Mewtwo 35 - It's like a Samus ditto, except the other Samus has less equipment. Honestly, you just outprioritize it. Out space, out prioritize, beat projectile with your own, don't get grabbed, don't get grabbed, and don't get grabbed. As long as Mewtwo can't grab you, he can't easily kill you.
Roy 30 - Crouch cancel.