Going to talk about the watchlist below, my opinions on them, and a bit more!
Blaziken
Yes, Swords Dance + Speed Boost on Blaziken is still disgusting. If it manages to get a Swords Dance, its snowball ability and just sweep through the opposing team is still too much. Its STAB attacks are supported very nicely by Earthquake or Knock Off, allowing it to take on, say, Toxapex or Alolan Marowak, which otherwise might be able to take on its STABs, make it overbearing.
Ban
Magearna
So I am very acquainted with Steel this generation, having played near 150 games with this type on the ladder since the DLC release. Magearna is still busted. With the insane support of Steel's defense, it just becomes way too easy to set this thing up safely. On top of the defensive resists/immunity they bring, Celesteela and Ferrothorn can provide Leech Seed support, easing the setup just that much more. Its most broken set is the Shift Gear+Calm Mind alongside Draining Kiss+Stored Power. Draining Kiss, while only 50 base power, is supported very well between it being STAB and Megearna's already high special attack. It can snowball very easily; additionally, it also makes Magearna harder to revenge kill as it restores its health.
Ban
Pheromosa
I think this thing will be broken when the metagame settles down more, but for now, I haven't seen it put in as much work as I think it will very soon. physical Adamant/Naughty nature Choice Scarf has to be the best set this thing has on both Bug and Fighting, with Close Combat, Triple Axel, or Ice Beam, Throat Chop, and U-turn. It can outpace, and OHKO Regieleki is super important as both types hard lose to that Pokemon under Electric Terrain. Aside from that excellent use of the Pokemon, I think thanks to Beast Boost, it will be too fast for anything to handle, and snowball attack boosts too easily. Will probably be problematic later on.
Potential Ban: This definitely has potential; I want to see it in the metagame after a few more bans.
Kartana
Ah, the paper cut, the airplane, the nuisance, Kartana. Any type that is weak to its STAB attacks or coverage will be very weak to its Choice Scarf set. I personally run Leaf Blade, Smart Strike, Knock Off, and Sacred Sword. This allows me to clean through a variety of types such as Ground (outside of Sand+Band Drill), Water (after a few layers of Spikes+Knock Off Toxapex can't switch-in), Ice (has Avalugg but can be worn down easily by Kartana's teammates), Psychic (since scarf Lati twins can't beat its teammates it easily wins that matchup with Knock Off+Leaf Blade), Ghost (scarf Gengar can be dealt with by many teammates, Choice Scarf Spectrier can probably put in work but has such bad coverage), and Fairy once Klefki is out of the match. While I have been using the Choice Scarf set, I believe Swords Dance can beat many fatter types without as many conditions met. I fully believe this is banworthy and should go
asap.
Ban
Zygarde 10%
This does not present itself as a problem for me right now. I think it is frail enough and doesn't have enough speed to become too difficult to revenge kill. After the metagame has settled with the true brokens out of the way, I think its worth looking at this Pokemon again.
Do not ban: I want to see this in a more balanced metagame before making my final judgments.
Naganadel
Without z-moves, this is immediately becoming less threatening than it was last gen. However, I do not think the lack of z-moves makes it not problematic. Its high special attack and speed allow it to snowball its speed, access to Nasty Plot, and near-perfect coverage (hits everything for neutral damage bar Heatran); it is too much. Let's dive into that a bit more. Nasty Plot allows its Draco Meteor's to still smash through everything it does neutral damage to, not named Specially Defensive Tyranitar and Blissey/Chansey. Fire Blast compliments this by hitting Steel-types like Celesteela and Ferrothorn, and Sludge Wave rounds them both out by hitting Fairy-type Pokemon such as Tapu Fini and Tapu Koko. On rare occasions, it can also be used to target the Water/Flying matchup by using Thunderbolt>Fire Blast, then becoming 100% impossible for the type to beat it.
Ban
Damp Rock &
Smooth Rock
Weather Rocks are never that healthy, in Monotype with 8 turns of Weather (especially damp because rain boosts Water STAB) is never healthy as teams aren't as equipped to deal with that say as in OU. Where any team can throw on a Corviknight and just wall Excadrill for days. Additionally, due to Monotype having access to a viable Gravity user in Landorus-I, sometimes even Ground immunities that resist STEEL are not enough to beat Excadrill. Smooth Rock makes healthy weather otherwise too overbearing. While it no longer has access to Mega Swampert, Rain still should not access Damp Rock. Being able to boost your STAB for that long and for free with Swift Swim users, almost for free spam strong Water STAB, is too much.
Ban:
Damp Rock- I do not think any Swift Swim user is a problem now; I'm not too fond of Urshifu-S with this being a thing.
Smooth Rock- I want to see this in a more balanced metagame before making my final judgments on it. But I definitely
still think this will for sure be problematic with Excadrill, especially now that Gravity Landorus-I exists again.
Terrain Extender
Electric Terrain abusers, specifically Regieleki, make this just too much for the tier. Ban it asap, not much more to say.
Ban
Regieleki
I also want to take this opportunity to talk about something else, Regieleki. This thing, while I don't think it is necessarily broken, is certainly unhealthy. What I mean by this is that under Electric Terrain, nothing aside, a Ground-type can wall this. By definition, that forces every type in the builder to throw in an Electric-type immunity, even if it is not the best possible choice, to not lose to this behemoth. Some types do not even have an Electric immunity to begin with. That means this thing will completely merk them without any outs. It can 2HKO even bulky resistances such as Ferrothorn. Types that Regieleki beats flat out are Fighting, Psychic (nobody should ever have to run Claydol, its garbage), and Bug. Types that need to include Electric immunities that shouldn't have to run them otherwise: Fire and Ghost (Lightning Rod Alolan Marowak), Electric matchups are unironically decided by this thing as well (the type that abuses it), Fighting and Bug (have to run Choice Scarf Pheromosa, but it'll be banned soon so its checks will not stay). I think this thing should be given a chance shouldn't be banned right now, but after the brokens are gone alongside Terrain Extender, its most definitely worth looking into for a ban.
Unhealthy: Ban Terrain Extender first; if it continues to be a problem, get rid of it.
Urshifu-R
I think Damp Rock makes this too much, but in general, Damp Rock makes anything that can abuse strong water stab too much. So I think the move here is to ban Damp Rock and keep a close eye on this.
Unhealthy: Ban Damp Rock first; if it continues to be a problem, get rid of it.
Steel Core
I want to say I've played an absurd amount of games with this core to start this off. This defensive core is absolutely nutty. I can not even begin to describe how insane it is. Even Blaziken can be defeated by them, as long as it is Toxic'd before it sets up a Swords Dance, these four forces mind games with even Blaziken to choose. On top of that, Ferrothorn and Celesteela provide Leech Seed support, promoting its defensive prowess. To take a piece from every generation of Monotype with Aegislash, I think the correct move is to reban it again. Even though Aegislash got nerfed this generation slightly, I do not think it has really affected its viability in the slightest. SubToxic sets make Aegislash so disgusting, backed by this core, that it should just be banned again.
Ban Aegislash: Going to past generations, the council has traditionally chosen to ban this to nerf the defensive Steel core. I think SubToxic Aegislash is the best set for this thing, and with the support that Steel provides