Samus: In Melee it used to be even, but as the metagame developed I thought the general consensus was that Fox slightly won (55/45 or so)? I play Melee and have a region filled with Samus' so it's one of my best MUs. Basically in Melee Fox can laser/platform camp and force Samus to approach, then counterhit her approach and win through rinse and repeating. All the Samus players (Knut, Minty, Boiko, Bubbaking) in my region say it's slightly in Foxes favor, and I agree. I play this MU extensively and have a good idea of how it plays out.
In PM though? Yeah Samus got some buffs, but she also got some critical nerfs concerning the Fox MU in particular. I play Boikos Samus so I have a decent amount of experience playing the PM matchup as well.
The ice mode buff in general is more or less useless against Fox because he's a fast faller/heavy so it doesn't kill any earlier than fire mode, and ice mode fair/dtilt just lessen the combo potential. Her boost ball is her main buff for the MU. Having boost ball makes it so she can avoid lasers pretty well, but at the same time she mitigates her mobility so it's easier for Fox to predict what Samus is going to do next. I'd call it a slight buff overall because it makes lasers easier to deal with, which is the main issue in the MU to begin with.
Fox also has new ways of dealing with Samus. In Melee, if Fox got a grab he had to uthrow and then shark uairs, try to stuff any options coming down with things like utilt, or just take positional advantage and force her to ledge. Now, Fox has a dthrow that's usable. Fox can dthrow tech chase regrab/usmash Samus at ANY percent. This goes for most characters you can't uthrow uair like Wario, Zelda, ROB, etc. in the game. The difference in PM physics means there's no shifted momentum when teching in directions so you can't hold a direction and tech that way to go flying in a specific direction like you could in Melee. THIS IS A HUGE BUFF FOR FOX. Fox can literally dthrow tech chase Samus until she's forced off stage like Sheik can do to Fox, except it's even easier because Fox is faster LMAOO.
Also, Samus has a super nerfed tether from Melee, which makes edgeguarding Samus in PM MADD easy. You just laser Samus as she's doing her down-b to get horizontal distance, then maybe go out for a shine to put her lower, and if she's below the stage you just wait for her to tether and punish it, and if she doesn't you can react to up-b by just shine bairing her and just rinse & repeat until she can't hit ledge anymore. After using her tether once, Samus can airdodge and tether to go really high (higher than her up-b) as a form of recovery, but she's in free fall without a hitbox going up so you can just react to it and punish that too.
Overall, I think the MU in PM is 55/45 for Fox because while she does have a way to get around lasers, she gets combo'd harder and edgeguarded harder than she did in Melee. I could see this becoming either easier or harder depending on how the metagame develops in the future.
This matchup is not just a repeat of a Melee matchup, it's very different in PM and very prone to changing as the metagame develops, so take my 55/45 with a grain of salt.
Edit: Something to note. Samus is way better in PM if she forces you to shield. If Samus comes off the platform and missiles and you shield it,she has a crazy mixup. She has the option to run at you and grab, run at your and fsmash/jab/ftilt, run past you and pivot grab, or run past you and crouch -> turnaround fsmash/jab/ftilt which is SUPER godlike.
If Samus had a way to consistently get Fox in shield I would think she wins the matchup, but with Fox having good mobility, quick aerials like nair to beat missile, and shine, Fox still wins the neutral in my opinion.