Protean Sweeper

Protean Mega Mewtwo Y is an extremely powerful setup sweeper with very few defensive checks. With its great speed tier; amazing coverage in Sunsteel Strike, Moongeist Beam, and Moonblast; and great mixed offenses, Protean Mega Mewtwo Y is one of the top offensive threats in the USUM Pure Hackmons metagame. It is not without flaws, however, as it is quite weak to priority before/as it sets up, being difficult to Imposter-proof, and while its defensive checks are limited, said defensive checks are notably common in the metagame. This set has many alternative options with their own pros and cons. These include (but aren't limited to) Life Orb over Focus Sash, which increases damage output but chips you every time you attack and leaves you unable to always live one hit in order to boost and KO back; Spore over Shell Smash in order to disable opponents and more reliably Imposter-proof, though this leaves you with a less potent sweeper; Freeze-Dry over Moonblast in order to hit Primal Kyogre, though this leaves you with a worse matchup into Slaking, as +2 Moonblast OHKOs it after Stealth Rock; and Extreme Evoboost over Shell Smash in order to make yourself more resilient into revenge killers, while making you unable to setup multiple times. If you're running a defensive Imposter-proof, use Naive to be slightly more resilient vs opposing priority. If you're relying on an offensive Imposter-proof, Hasty is preferred to make Imposter take more from your own priority.

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This Pokemon is useful for dealing with unboosted threats, notably Mega Mewtwo X, due to its high offenses and speed. This Pokemon can also deal with stall teams notably well, due to its few and far between defensive checks and said defensive checks being somewhat unreliable.

Protean Mega Mewtwo Y prefers to be on more offensive teams, as defensively Imposter-proofing it is very difficult. Pairing it with Regigigas is a good option as more offensive teams appreciate the priority that Regigigas provides, and Regigigas can offensively Imposter-proof Mega Mewtwo Y while being able to take a Sunsteel Strike or Moonblast from Imposter. Stealth Rock setters are also helpful for Mega Mewtwo Y, as breaking Focus Sashes is very helpful for it, and Stealth Rocks heavily cripple Ho-Oh, letting it break through easily.

• Arceus, Primal Kyogre, and Ho-Oh: These Pokemon can check Mega Mewtwo Y with a combination of their stats and defensive typing. Wonder Guard sets can be broken through easier, though can still prove troublesome due to them commonly running moves such as Sacred Fire and Steam Eruption. Prankster variants of these Pokemon can prove especially problematic, though, leaving you with little to no options other than running teammates to cover these threats. Thankfully, these Pokemon aren't dedicated physical walls, so Huge Power attackers, especially Mega Mewtwo X, can beat these nicely.
• Regigigas: Opposing Regigigas can be difficult for Protean Mega Mewtwo Y, as they can tank Sunsteel Strike or Moonblast and fire back with Extreme Speed if you're Normal or Fairy type or miscellaneous coverage if you're Steel type. Luckily, there's a vast amount of checks to Regigigas, so Sunsteel Strike walls like Mega Scizor, Mega Swampert, Wonder Guard Primal Groudon, etc, can easily switch in on the vast majority of Regigigas sets.