BAN SHELL SMASH
I don't know how anyone can argue that Shell Smash isn't the big problem here. Not the anti priority abilities, not psychic surge, and not Focus Sash. I've said it before, but it's like two pages back so I don't feel bad about saying it again.
If you run an antipriority ability, no other setup move increases both offensive stats as well as speed, and not even by two stages. There really is none. The closest things we have is simple z celebrate, Power Herb Geomancy or z geomancy, and both of those require an item to use. The big problem with Shell Smash is that your item AND ability slots are both free, and what differentiates it from any comparable setup move. Special walls can wall Quiver Dance, and physical walls can wall Shift Gear sets, but no mixed wall can beat Shell Smash combined with anti priority. But the anti priority isn't really the problem, it's that the smash user hits too hard to be stopped. If we banned antipriority, we'd probably have to add an -ate clause to keep --ate users in check like we did last gen. And it's not like banning Shell Smash will stop setup. There will still be Quiver Dance, and z geomancy and swords dance and Shift Gear and they'll probably actually get use a lot more if that Shell Smash is banned because, why not get a +2 boost to speed and +2 to all your offensive stats so you can simply kill whatever needs to be killed before it even has a chance of hitting you? That's how shell smash works. Put it on any offensive mon, and it becomes four times as threatening. Oh and Prankster Haze won't really stop you, as the haze user has to 1) wall you, and then 2) is basically locked into clicking haze until you don't click Shell Smash and then you have all the momentum to switch to whatever you want.
If you want to play even more high risk high reward, you can run Shell Smash with Simple to double your boosts, and perhaps a White Herb so that you have 3x attack, Special Attack and Speed without any negative defense. Good luck revenge killing that; it isn't going to happen if the smasher has 100% health, which it should have once your opponent's team has been sufficiently weakened. Power Trip has 260 bp and KOs everything without unaware. If you add Sunsteel or Moongeist beam, the only thing that walls you is Unaware Mega Gyarados, and you can easily chip that down into 2hKO range Again, not even Simple z Geomancy can compare to simple shell smash, since the opponent has a free turn to haze or topsy turvy your boosts. I just don't get how people can be arguing that Shell Smash isn't the broken element here, but if someone wants to argue for it, I would like to hear it.
I agree that Shell Smash is broken, and I think you forgot to point out these:
* Defense drops become irrelevant when paired with Focus Sash and Anti-priority.
* Imposters are also forced to play Russian Roulette speed tie game because Eviolite Boost is nullified by Defense drops, unless they are running rare Choice Scarf.
* Innards Out, if it has to be used as a last ditch effort to stop sweep, will be used with least efficiency of eliminating that sweeper left with 1 HP.
But what I do not agree is:
* White Herb or Simple leaves the user VERY vulnerable to Imposer unless they are running something like Unburden and Imprison, which is completely walled by Prankster Haze user.
*
I insist upon applying Item Clause (probs 1 or 2 each) but most people do not agree with it so I would say
Ban the combination of Focus Sash and Anti-Priority.
Shell Smash becomes pretty useless without Focus Sash.
Will MMY survive Pdon's V-create after Shell Smash boost?
Will Deo-A survive Registeel's U-turn after Shell Smash boost?
Will Mega Rayquaza survive MMY's terrain-boosted Psystrike after Shell Smash boost?
Or,
Will MMY survive Kyurem-B's Refrigerated Exspeed after Shell Smash?
Will Yvetal survive Zekrom's Galvanized Exspeed after Shell Smash even if it has White Herb?
So yes, Shell Smash is a problem. Everything you have mentioned (
Anti-Priority, Shell Smash, Focus Sash) is a problem. But they are problems when they are linked to one of the other.
This user named
Watatatata in PS! is circulating around ladder between 1550 and 1600. I have seen him play, and he has 4 'mons with Focus Sash and 2 Pranksters with Destiny Bond, which requires literally an inch next to no skill to use. 2 of those Sash 'mons have Shell Smash and one of them has Magic Guard with Rapid Spin. If he lost to someone, he stalks that person, memorize his team, and stall out until his opponent's win factor is gone.
Play one game with him, and you will entirely agree with me and SuperSkyLake.
So why do I mention about this user? Well, is it healthy for someone to simply and effortlessly break through teams by spamming Shell Smash with Focus Sash? This is what ShedMiddleFinga said in one of his battles when someone asked him his thoughts about Shell Smash:
"F**k Shell Smash, get the skill first."
Although we both win and lose to each other back and forth, I highly respect him as a player not only because he has excellent senses, but because he keeps his team in a form of Gen 6, which means that he purely climbs the ladder using his predictions and good team building skills. (Although him using Assist Pdon team is quite contradictory to this)
Imagine how frustrating would it be to lose against someone with 4 'mons with 2 DQM / 2 Psychic Surge with Focus Sash spamming Shell Smash until your walls are gone.
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If you wish this metagame's ladder to be based on who has more Sash-Smash spams, or think I am conspiring against the forum, you can stop reading here.
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I understand this is in OM's category but I do not want this meta to be no-skill meta.
Why do we have Wonder Guard in a banlist? Because we don't want to see Wonder Guard Air Balloon Manectric behind Substitute sweeping.
Why do we have Huge Power in a banlist? Because we don't want Rayquaza to demolish everything with Dragon Ascent outsides Fur Coat users.
What have we banned this Gen so far?
CFZ's, because all you have to do to sweep with CFZ's is knowing how to click with a finger.
What are we suspecting?
Water Bubble, because it is almost impossible to wall outsides Water Absorb, but even this sometimes fail to check Water Bubble because of Core Enforcer.
We have to make more thoughts about which factors among
Focus Sash, Anti-Priority, and Shell Smash, and decide which one is the most problematic or which 2 or probably all of them cause problems when they are stapled together.