At first glance, Duosion seems like a rather underwhelming Pokemon, even for RU, due to its somewhat lackluster base stats and weak defensive typing. However, despite these factors, Duosion is undeniably an extremely threatening Pokemon. Eviolite grants it a huge amount of bulk, Magic Guard offers it an immunity to all of the hazards and other forms of passive damage, and it has a massive base Special Attack stat. Thanks to these factors, along with its solid offensive coverage and decent support options, it has the ability to be an effective Pokemon in RU.
Although it lacks the excellent typing and Speed that some of the other Calm Mind sweepers in RU possess, Duosion can pull off an effective Calm Mind set and should not be taken lightly. Having reliable recovery, near perfect coverage in two moves, and most importantly, Magic Guard, Duosion is a significant threat in the RU metagame. Reliable recovery and Magic Guard are especially important because they're really all Duosion has over other Calm Mind users such as Musharna. However, those two things are easily enough to distinguish it from its competitors.
Calm Mind boosts Duosion's already massive Special Attack stat sky-high while also increasing its respectable Special Defense stat. Recover pairs beautifully with Calm Mind, letting Duosion sponge special attacks easily after a boost while taking advantage of its solid Defense stat, and making Duosion ridiculously difficult to beat in general. Either Psyshock or Psychic should be used in the third slot, each having its own advantages and disadvantages. Psychic is usually the better option, hitting most Pokemon in RU far harder than Psyshock, but using Psyshock allows Duosion to beat Cryogonal and win Calm Mind wars. Thunder is Duosion's best coverage move, as it unfortunately does not learn Thunderbolt. Thunder grants super effective coverage against dangerous Dark-types such as Crawdaunt and Drapion, as well as bulky Psychic-types such as Slowking and Sigilyph. It also boasts a handy 30% paralysis rate, and Duosion is bulky enough that it can afford an occasional miss. Hidden Power Fighting is an option to hit Steel-types harder, especially Steelix, who can phaze away Duosion's boosts, but it leaves Duosion utterly walled by Pokemon such as Spiritomb and Sigilyph.Team Options & Additional Comments >>>
Duosion can easily pull off an offensive Trick Room set similar to the one that its older brother, Reuniclus, uses in OU. With this set, Duosion can clean up teams late game with ease, thanks to its high base Special Attack stat and access to perfect type coverage between Psychic, Hidden Power Fighting, and Shadow Ball. Magic Guard, along with Duosion's passable defenses, also play a part in this moveset, letting Duosion easily switch in against and threaten almost all offensive teams, while also letting it blow holes in most common stall cores.
Trick Room is naturally the crux of the set; with its solid defenses, Duosion can switch in on a number of threats and then proceed to set it up. After that, Duosion can abuse its ridiculously low Speed to outspeed nearly the entire metagame under Trick Room. Psychic is Duosion's main STAB move, and hits many common Pokemon in RU for decent amounts of damage. Shadow Ball hits opposing Psychic-types, while Hidden Power Fighting rounds off the moveset by giving Duosion perfect neutral type coverage and most importantly, allowing it to hit all of the Dark-types who would otherwise give it trouble.Team Options & Additional Comments >>>
Duosion possesses an excellent support movepool, consisting of a variety of solid options such as Thunder Wave, Trick, Toxic, dual screens, and Rain Dance. However, Duosion doesn't particularly abuse any of them very well; Uxie is usually better for general support thanks to having access to Stealth Rock and U-turn anyway. Also, in order to effectively use dual screens or Rain Dance, Duosion can't use Eviolite, which significantly decreases its bulk. Duosion can use Trick on some gimmicky sets with Flame Orb, but Clefable can pull Trick Orb sets off better.
Duosion's offensive movepool is pretty sparse, consisting of the bare minimum of STAB moves and Hidden Power. However, it does have access to Flash Cannon and Energy Ball, but they don't provide any important type coverage that isn't already covered between Hidden Power Fighting and Shadow Ball. Duosion also has access to some physical moves, such as Explosion and Gyro Ball, although it can't hurt anything with them due to its base 40 Attack.
Checks and Counters
Thanks to Duosion's high Special Attack and massive bulk, it can be difficult to switch in on. However, most Dark-types, such as Drapion, Crawdaunt, and Zweilous, are capable of picking off weakened Duosion without too much trouble. Drapion and Skuntank are especially effective in countering Duosion, as unlike other Dark-types, they don't have to worry about being hit hard by Hidden Power Fighting or Thunder. Strong physical attackers who aren't hit super effectively by Psychic or Duosion's common coverage moves also make good answers to it, since they can switch in and power through Duosion without too much trouble. Similarly, if it hasn't boosted its Special Defense, most powerful special attackers, such as Moltres and Sceptile, can break through it.
Duosion has to be wary of Pokemon with Trick and Knock Off as well, as no matter what moveset it's using, it gets a significant amount of use out of its item. Calm Mind Duosion without Eviolite and Offensive Trick Room Duosion without Life Orb are both much less threatening than they would be with their items. Pokemon with Knock Off include Mesprit and Tangrowth, while common Pokemon with Trick include Manectric and Rotom.