Hmm, first time I see this meta. Looks interesting, there are lots of possibilities. One thing I notice though, why would Stall EVER be good in a meta where Magic Guard is Share-able? Magic Guard is pretty much mandatory in HO because,
1. It gives you Recoil-less LO
2. Make strong recoil moves like Flare Blitz, Head Smash, well, recoil-free
2. Ignores hazards and damaging status
So, because of this, you can just slap a MG mon + 4-5 strong wallbreakers with stacking abilities and it will do well vs Stall. No matter what, with Magic Guard you can't be PASSIVELY worn down whatsoever, while in general, Stall's goal is to wear you down PASSIVELY. The only hope for Stall to exist is through PP-stalling, that's it.
Regarding Multiscale, is it broken? Well, it won't be broken in Stall for sure, but Magic Guard basically makes you ALWAYS have 100% health first turn, so it may be another necessity for HO to live a hit when it's HO vs HO. I can see it being broken in that regard.
Stall exists through PP stall, and is actually viable that way. Against a team that doesn't quite hit hard enough it can literally just keep switching with regenerator and never lose. Unaware stops setup, Magic Guard stops hazards and status, Regenerator gives you the passive healing, and Multiscale means that your opponent effectively has to be able to do 73% to your Pokémon in order to break through (to break that Multiscale you have to do over 33%, which means 66% normally, and you add Leftovers to that). And then you add Pressure to make it even worse. You can even add Shell Armor or Poison Heal to it. Now, I don't like Poison Heal as much because I enjoy running Toxapex on these teams, but you could remove Pressure to add Corrosion in and run a Toxic Orb. Great
meme strategy! Marvel Scale can also be added to that for more bulk. So stall is pretty good, but has its checks. And its biggest check is Mega Gyarados, which can set up with Dragon Dance and break through the Unaware. But it looks like Mega Gyarados is going to go, which will make stall even better. But for now it is a great check. However, I have tried using Intimidate to counter it. Now, normally Intimidate is useless because Unaware will ignore the attack drop. But Mega Gyarados ignores Unaware, so the attack drops will be there. Now a Substitute set could beat that, but just add an Infiltrator mon!
Another thing stall loses to is extreme HO. It can often break through Multiscale and destroy any stall team. However, a Substitute+Protect+Poison Heal+Pressure+Dazzling+Prankster team could potentially beat that. You can't outpriority the Prankster Substitute, and you can just PP stall by clicking Substitute and then Protect.
Finally, Multihit HO can demolish Stall. You break through the Multiscale and any Substitutes, and do massive damage. Skill Link+Technician=187 Bullet Seeds, Rock Blasts, Icicle Spears, and Pin Missiles.
And that's a basic summary of stall. Now for my thoughts on Magic Guard and Multiscale.
Magic Guard is almost a mandatory ability for teams. As Chopin mentioned, you are immune to Hazards, Status, Life Orb recoil, and Recoil Damage. It also allows for Multiscale and Sturdy to remain intact. It completely invalidates Iron Barbs, Rough Skin, and Rocky Helmet, and gives you no Mind Blown health loss, no Solar Power damage, and no Dry Skin HP loss from sun. You are not damaged by Whirlpool's passive damage, and you ignore Leech Seed. So there's a legitimate argument for banning it. But I'm against it because bans can be a slippery slope. Ban Magic Guard, and Ferrothorn+Garchomp invalidates any physical attacker. It makes Hazards good again, and would destroy Multiscale and Sturdy. Now that's not necessarily bad, but it could improve a lot of Hyper Offense, potentially to the point of being too good. It would also destroy a lot of HO. All in all, it would drastically change the metagame.
Now, Multiscale also has an argument for banning it. Hyper Offense doesn't run it as much because Hyper Offense beats Hyper Offense via other methods such as Dazzling, Psychic Surge, Sturdy, and outspeeding. For example, an Unburden Psychic Surge with Sturdy team beats a Brave Bird Priority Team or a Triage team, but loses to Multihit with Sturdy or opposing Terrain. It also loses to stall. Multihit teams lose to Priority teams, but with Bruxish they counter them. It's a complicated RPS system. Now, a Multiscale ban would also have large repercussions on the metagame, but possibly less so than Magic Guard. I am still not in favor of it because it would make Sturdy even better and destroy bulkier teams, which are necessary to counter Unburden teams.
Now, Dazzling is another extremely common ability. Depending on the team it can be better or worse than Psychic Surge. But overall it destroys a lot of team archetypes. However, I would still not ban it.
So that's my opinion on some of the best abilities and strategies in the metagame. I'm working on a HO guide so I can post that soon too. Hope this was helpful!