E4 Flint
Moldy Moves:
It would need to be established that the overall coverage and properties of the MoldMoves make them broken when used with most varieties of setup and in general play.
First on Coverage: I would say Photon Geyser getting STAB can be more beneficial than having good coverage for MMX, and MMY. In regards to the properties of the moves, Photon in particular can allow MMX to switch from physical attacker to special attack via Fleur Cannon alone.
In regards to their coverage in General, if Moongeist Beam didn’t handle Ghost and Psychic-types, then Superpower would be much easier to wall. Just imagine Flash Fire Steel-Types like Aegislash walling both V-Create, and Superpower, leaving only a resisted Photon Geyser to hit from the physical-side.
252 Atk Life Orb Mewtwo-Mega-X Photon Geyser vs. 252 HP / 252 Def Aegislash-Shield: 83-99 (25.6 - 30.5%) -- guaranteed 4HKO
Fleur Cannon certainly wouldn’t do enough...
252 SpA Life Orb Mewtwo-Mega-X Fleur Cannon vs. 252 HP / 252+ SpD Aegislash-Shield: 56-66 (17.2 - 20.3%) -- possible 5HKO
Their properties alone don’t make them broken, but their use in combination with other boosts from Abilities, Attacks and items can push them over the edge when all factors are combined, for Contrary, and with Simple. Afterall, how many Pokémon cannot serve as an Unaware check due to Moongeist Beam alone?
Psychic is walled by Psychic, as is Fighting, but MMX can just use Moongeist Beam to bypass Psychic checks. Otherwise Defensive Psychics like Cresselia would be a prominent Unaware Wall without fear.
Audino-Mega cannot serve as an Unaware or Fur Coat Defensive Check when the foe packs Sunsteel Strike.
The fact that Unaware Gyarados-Mega is a thing is testament to the level of coverage they provide, as there is little, if anything, without that typing that can withstand Moldy Moves. The next closest option would be Fire/Dark, and those Pokémon like Incinaroar just don’t have the Defensive Stats to tank those hits.
Personally, I think it's difficult to argue this point. Contrary + MoldMoves complex clause is not to be considered, MoldMoves, Contrary even without them has been discussion worthy as the power creep makes the Contrary moves hit harder than they used to, even if we ignore the increases to their stats and treat every hit as +0 or an increase to Speed only.
That’s not true, all -2 SpA Offense moves (besides Psycho Boost) lost 10 Base power in the generation shift between Gen 5 & Gen 6. 10 Base power seems small, but after STAB, that becomes 15, and the gap widens after each +2 SpA boost the Pokémon get. Afterall, we still had Kyurem-White at 170 Base SpA in Gen 5, so let’s not pretend it was strictly the base stat points that drew the concern for power creep since then. Back then we also didn’t have Fur Coat, and Fairy types to freely switch into V-Create / Superpower or Draco Meteor, respectively, so imagine Draco Meteor Kyurem-White back then... a much bigger threat than now.
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Did we forget Imprison?
Imprison on a Contrary user, especially when paired with Special Attacks and V-Create to minimize Struggle Damage, can Effectively Counter Imposter.
Photon, V-Create, Fleur Cannon, Imprison on MMY effectively uses Photon to bypass Sturdinja, and Unaware, while Fleur Cannon boosts its SpA, V-Create adds speed and defenses to handle faster threats like Beedrill-Mega, and to tank priority.
Imprison blocks Imposter, and quite frankly, many other Pokémon from using V-Create on their sets.
I don’t think everyone should advocate for Imprison. But I could see it’s use for counterplay on Imposter and other Contrarians (like MMX).
Edit-
Rumors just read your post mentions it, but couldn’t get thru your entire post- initially.
We don't need to worry about the next best thing unless it's extremely similar, that's now how suspects/bans work. Like, if we were going to ban Slaking for whatever reason, then discussing it without including Regigigas would be a bad idea, yeah. But exceptions like that are extremely few and far in-between and the only one I can think of that ever actually came up was Magnet Pull in the Gengarite discussion.
Besides, if we wanna get literal, the most Contrary-like non-Contrary thing would be (Simple) Power-up Punch.
Also, because I forgot to mention it earlier, but obligatory "You guys should really look at X/Ytwo sometime because guess who's at the forefront of abusing the current item of suspicion again!" Don't let this line veer discussion away but, seriously, can we at least talk about these guys sometime in the future after we decide on suspecting Contrary or not? Doesn't need to be next but, you know, someday would be good.
I think the difference between Simple Power-Up Punch and Beast Boost is that Beast Boost allows you to get a boost off of any finishing move, while a Ghost-Type can Wall Power-Up Punch like it can Superpower.
Beast Boost can also allow you to change the stat you want boosted. So if Hasty Necrozma-Ultra uses Psycho Boost to KO a foe, after the stat is lowered, it gets +1 Attack and then next turn uses Photon Geyser off of its Attack stat, it can mixed sweep, and likely get a second KO with the new boost, effectively letting it get to +2 Attack.
I think that what makes Simple limited is that it cannot Snowball as easily. Plus, 40 Base power? Shell Smash works better, but requires White Herb to avoid -2 Defenses.
Anyways, I don’t think Beast Boost or others are broken, afterall no one really uses them now... but I could see them rising to help replicate what Contrary does- Boost without losing momentum.
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I think we should also mention which Pokémon besides the big three benefit from Contrary:
So besides Rayquaza-Mega, Mewtwo-Mega-X, Mewtwo-Mega-Y, we also see Sceptile-Mega, Blaziken-Mega, and Necrozma-Ultra.
Is there any another Contrary user we may have missed?