Masquerain looks like yet another generic Bug- and Flying-type Pokemon, but he has a few tricks up his sleeve that might surprise you. He distinguishes himself from other Pokemon with identical typing by his somewhat superior special movepool, which includes two attacks that are more commonly seen on Water-types—Hydro Pump and Ice Beam—as well as an excellent ability in Intimidate. Intimidate is very helpful, since it allows Masquerain to switch into a slew of physical moves that he wouldn't be able to handle otherwise, despite Masquerain's poor defenses. Hydro Pump and Air Slash together hit every Pokemon in UU neutrally except for Lanturn.
Unfortunately, Masquerain is still a mediocre Pokemon, as his horrendous typing and stats hold him back from doing much at all. Being 4x weak to Stealth Rock hinders the usefulness of Intimidate, while his low Speed and Special Attack make his excellent two-move coverage in Hydro Pump and Air Slash not as great as it could be. All in all, Masquerain is a fairly unique Pokemon that, despite horrible, crippling flaws, can be quite useful to your team through proper support.
Speed is often an issue that plagues Masquerain. Base 60 Speed is quite low, and because of this, Masquerain cannot normally sweep very well at all. Fortunately, Masquerain can utilize Agility to substantially help his chances of ripping through the opposing team. Even if Masquerain cannot plow through defensive Pokemon due to his low Special Attack, he can still prove to be an excellent member of the team due to his ability to Baton Pass Agility boosts.
Agility allows Masquerain to reach a very respectable Speed so he can attempt a sweep. Thanks to Intimidate, it isn't too difficult to use Agility either. Air Slash is for STAB and good coverage, while Hydro Pump complements Air Slash to form an excellent attack combination that hits almost everything in UU neutrally. Roost can be used instead of Hydro Pump if you wish to give Masquerain some longevity, but even with Intimidate, Masquerain isn't that bulky. In the last slot, Baton Pass is recommended since Masquerain will often lack enough power to muscle through Pokemon that wall him, such as Milotic, Registeel, and Chansey, so instead, Masquerain can pass the boosts to a teammate to allow it to sweep.Team Options & Additional Comments >>>
Masquerain's movepool is quite good, and contains quite a few decent special attacking options that can be used instead of Hydro Pump. Energy Ball, Shadow Ball, Hidden Power Ground or Fighting, Ice Beam, and even Blizzard can be useful in assorted scenarios. However, they provide mostly redundant coverage with Air Slash and Hydro Pump. Silver Wind or Ominous Wind can be used if you think you can get lucky with their secondary effect, but they are generally too luck based to be used.
Masquerain is capable of using a more defensive set that abuses Stun Spore and Air Slash alongside Roost, but Masquerain is often too frail or too weak to use it effectively. Haze is an interesting option to remove stat boosts, but Masquerain's poor defenses prevent him from effectively countering stat-boosting threats. Masquerain can use Rain Dance, since his Hydro Pump benefits from the rain, but Masquerain doesn't really have amazing synergy with rain sweepers aside from resisting Grass-type attacks, and he can't use it well due to his poor defenses.
Finally, Masquerain can use Choice Specs or Choice Scarf to boost either his Special Attack or his Speed, respectively. Masquerian becomes quite strong after a Choice Specs boost, and with two very good attacks to spam in Hydro Pump and Air Slash, he can be a decent threat. Sadly, being 4x weak to Stealth Rock, having few good immunities and resistances to switch in on, and a low base Speed stat makes Choice Specs a mediocre option. Choice Scarf can make Masquerain fast enough to outspeed some Pokemon, but with only a base 80 Special Attack to fall back on, Masquerain is generally too weak, and many of the issues a Choice Specs set would have are present here as well.
Checks and Counters
The bane of Masquerain's existence, like every other Pokemon that is 4x weak to Rock, is Stealth Rock. With Stealth Rock chipping off 50% of his HP every time he switches in, Masquerain will have little chance of switching in successfully. Keeping Stealth Rock on the field will result in Masquerain being mostly dead weight on your opponent's team.
If, for some reason, Stealth Rock is not on the field, Masquerain can prove to be quite a nuisance. To counter Masquerain, any reasonably specially bulky Pokemon will do, such as Registeel, Chansey, Clefable, and Milotic. It is also noteworthy that the first three can set up Stealth Rock to hamper Masquerain, and can use Thunder Wave to nail any potential Baton Pass recipients. However, these Pokemon aren't a guaranteed stop to Masquerain, since he can easily Baton Pass to a Ground-type such as Rhyperior or Torterra to absorb the Thunder Wave, and that Speed-boosted teammate could then easily rip through your team. Because of this, the best counter to Masquerain is Haze Milotic. Haze Milotic doesn't care about Masquerain's weak attacks, and can easily remove any Agility boosts that he tries to Baton Pass.
Bulky Pokemon that use Substitute can be a nuisance to Masquerain. If the Pokemon uses Substitute as he Baton Passes, the Pokemon behind the Substitute can react easily to the Baton Pass recipient. Mismagius and Rotom are good choices for this strategy, as Rotom will often scare Masquerain off with the threat of Choice Scarf Thunderbolt, while Mismagius is fairly bulky, and after a Calm Mind, Masquerain will be hard-pressed to break her Substitutes.