I doubt Azumarill would be as good as your fear as is giving up on its ability so anyway, you know this format existed in the past, right? Feels weird that you didn't mention it, so just want to make sure: https://www.smogon.com/forums/threads/dual-wielding.3608611/I hesitated on posting this concept; there's a rule on "Hoarding" that OMs that revolve on holding X amount of items is likely not to be accepted, but I wanted to submit this idea for the sake of knowing if this is, indeed, frowned upon or if it's an idea that can be done.
Anyway:
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Dual Wield
"Twice the utility! Twice the power!"
Metagame premise:
Sacrificing your Ability slot will grant you almost any item (no duplicates) that can't be knocked off or swapped. A Pokemon could hold both a Expert Belt and a Choice Scarf to boost the power of their moves along with their speed. Abilities that replace or copy will not work on dual wielders, and moves like Corrosive Gas will fail to delete the "abilitized" item. Perishable items cannot become your secondary item.
I imagine this will be a much more chaotic metagame where offense becomes fast and/or stronger and defense becomes heartier (Black Sludge + Leftovers stall?).
The metagame is OU-Based. Terastelization is allowed.
Potential bans and threats:
•Choice Band/Specs (Potential Ban)
I would probably ban the attack boosting items immediately. In short; avoid Gorilla Tactics if possible. In detail, I avoid Choice Scarf since it doesn't necessarily define or break a Pokemon if it doesn't have the ability to hit hard in the first place. Could be relooked at, but I'm more willing to ban first then re-evalulate.
•Leftovers (Threat)
Suddenly, Life Orb becomes less threatening with recovery at the end of every turn. Simply put, health = good, especially when that health is ensured thanks to Knock Off not working on the second slot.
•Life Orb (Threat)
1.3x power in exchange for health can become problematic when the cons can be balanced out with the aforementioned recovery of healing items. It can also compound with type-exclusive items, making for some really nasty STAB moves.
•Light Clay (Potential Ban)
•Damp/Smooth/Heat Rock (Threat/Potential Ban)
•Corviknight (Threat/Potential Ban)
Corviknight can run many solid items that can hypothetically make it nigh unstoppable. It's abilities were never the greatest, though usable, but now it can use an arguably more beneficial item to support it exponentially. It can potentially use items like Leftovers, Heavy-Duty Boots, Covert Cloak or a Rocky Helmet to further compliment itself. I'm unsure of how gameshaking Corviknight could be, hence I'm on the fence of threat or ban.
•Toxapex (Threat/Potential Ban)
See Corviknight, it's similar in every way but the abilities are amazing and it'd rather run Black Sludge over Heavy-Duty Boots (I think). It being capable of using two passive healing items may be a problem, I suppose.
•Great Tusk (Threat)
If GT sacrifices its Protosynthesis ability (thus making Booster Energy unusable), it can probably run Heavy-Duty Boots + Life Orb to be able to switch in safely and deal damage accordingly. I am unsure to how well this will do in this metagame, but come on. It's Great Tusk.
•Gholdengo (Potential Ban)
Gholdengo can do exactly what it usually does – switching Choice Scarf to it's opponent – but can now be unscathed by hazards entirely with HDBoots or boost the power of its moves with Life Orb, keeping it healthy in the process with Recover. Though hazards are deterred in this kind of metagame with how common HDBoots will probably be, it's even more impossible with Gholdengo running around.
•Kingambit (Potential Ban)
Black Glasses + Life Orb/Choice Band + Adaptability/Supreme Overlord makes Kingambit's overwhelming power even more absurd.
•Azumarill (Potential Ban)
A traditional set with the capability of adding Life Orb to it.
•Shell Smash (Threat)
"But Sense!", says yourself, "I thought you said perishable items can't be your secondary slot!" Well, true. But that just means that your primary slot could, in theory, be a regular item (knockable and all), thus allowing it to be perishable, and you allow your secondary slot to be anything-but. For example, say your item is a White Herb, allowing for traditional Shell Smash antics, but now you can use Life Orb as well, drastically boosting your power in the process. Hence, the threat. But it very well can be a ban, I just see it as less problematic.
Though not problematic; I'll also mention that Mental Herb can be used on hazard setting leads to ignore Taunt, while still allowing it to run Covert Cloak, HDBoots, Rocky Helmet, et cetera.
•Weakness Policy (Potential Ban)
As previously stated, it can't be the secondary item, but another move can. Activating the policy can be devastating.
Bans:
•Revival Blessing
Leppa Berry now doesn't restrict your item slot, so you can run Choice Scarf on Pawmot to outspeed most Pokemon and revive a teammate for essentially free. It's banned in other metas, and this one would be no different.
Questions for the community:
•Are there any potentially broken Pokemon I could have missed?
•Should the secondary item be protected (can't be knocked off/switched)? If not, how would de-itemizing moves react to the second item?
Note: Making it unable to be removed seemed the simplest way to justify not overcomplicating the base game. Any move used that would otherwise effect the item would only effect the primary item slot.
•I stated that perishable items; items that are used up upon activation; would be restricted from the secondary slot. In concept, it would not only leave the user without an "Ability", but it'd be complicated to allow two perishable items on one Pokemon (how would they interact, what takes priority, etc.) Should this restriction be lifted?
•Would this metagame be too beneficial to one style of battling (hyper offense vs hyper defense/stall)?
•With how insanely strong a Pokemon can become in this metagame, could this be an Ubers-based metagame? Further, would they too get the gimmick of two items, or would they be restricted from the rule for balancing ( ala. Mix and Mega's Ubers)?
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A bit unsure of if this is encouraged as an OM submission. Feedback requested and appreciated.
I don't really agree with your planned bans for the most part, Revival Blessing doesn't seem like that big of an issue, Pawmot has to survive in the first place while doing the most obvious play and use the move twice for it to make any difference compared to standard.
Don't see what is bad about some good walls being able to use the mechanic? Corv and Pex still just do what they always do, and their problems still exist, everything else is powering up the same way, so it just balances out.
Banning stuff like Life orb and Leftover may just kill the format as there isn't that much when it comes to items to choose, the format had some popularity problems back then as you see in the thread that after 2017 the thread kind of just died, and without Z-Crystals and Mega Stones we have way less options now.
And about the ubers... It just doesn't make much sense, you have to think if the rule changes do anything to balance them, in MnM works because the average BST of megas is similar to base cover legends making them comparable in strength, and similarly, I think that going with an "OU based" mindset is the wrong way to look at a format's banlist, the starting banlist being a copy of OU is usually fine as we are just figuring out how stuff works, but afterward is better to make any needed adjustment and ignore if something is OU or Uber or whatever and just look at the environment of the format you are playing.
But either way, don't really see a need for this format to come back, we may have a bunch of cool new items, but without Z-Crystals and Mega Stones I can't see it being all that interesting, it sounds like a toned down trademarked.