Disagreeing with moving Mandi down. I've been using its specially defensive set on a balanced team and it's performed exceptionally well. It is so specially bulky that I've found that its SR weakness does not hinder it that much at all; it can still switch into even the likes of Hydrei's Draco Meteor and Roost off the damage quite comfortably. It isn't even 2HKOed by defensive Florges, and this is from a Pokemon that has 112 base Special Attack. The amount of utility it provides is incredible with Knock Off, Taunt, and Defog, and it's an amazing asset to have against defensive teams as it can prevent them from setting up hazards, cripple their walls, and remove any hazards that do go up too. Overcoat shuts down Rose and Amoonguss as well.
The physically defensive set, meanwhile, is amazing against offensive teams in conjunction with Foul Play. It works quite similarly to physically defensive Umbreon, being able to take even the most brutal physical hits and OHKO them back with their own power. The only downside to it that I've experienced is it being complete set up bait for Cobalion and Lucario, which can spell the end against offensive teams if it's late-game and the rest of my team has been worn down. It's also vulnerable to status, and it's annoying being burned by Scald when trying to prevent defensive Water-types from using support moves, so I paired it with Florges to heal any poisons or burns it is afflicted by.
Overall, considering its few downsides and its ability to provide tremendous team support, I think it fits quite well in A-.
Agree with moving Chesnaught down, it is a beast physically but it is really hindered by its weakness to the secondary typing of common physical attackers, such as Flying (Mega Aero), Ice (Mamoswine, Mega Abomasnow), Poison (Mega Bee). Several other physical attackers who it could potentially wall also carry coverage moves that can significantly hurt it (Ice Punch Gatr and Mega Pert, Fire Blast Salamence). I think B+ is the ideal place for it.
Toxicroak moving up is an interesting one. The ability to heal up using Scald can't be understated with the move everywhere, and I'm a huge fan of the bulky Swords Dance set which can be hell for defensive teams to face as it can continuously heal itself with Drain Punch. However it does come up short against quite a few Pokemon, namely bulky Psychics and Ghosts, and Mega Aggron. An all-out offensive set with Life Orb can break through the aforementioned Pokemon though, seriously a +2 LO Gunk Shot packs insane power:
+2 252+ Atk Life Orb Toxicroak Gunk Shot vs. 252 HP / 252+ Def Cresselia: 308-364 (69.3 - 81.9%) -- guaranteed 2HKO after Leftovers recovery
This set is a lot frailer though, and the lack of Black Sludge can affect its capability to tank random Ice Beams and the like.
Against offense though, Toxicroak fares pretty poorly in my experience. It can't set up due to its frailty and its Speed is not great. Sucker Punch is also not a reliable priority move at all, and a lot of common offensive Pokemon such as Lucario, Hydreigon, and Krookodile resist it. All things considered, I think its positive attributes are worthy of a rise to B+, but A- is a step too far.