Amoonguss's excellent bulk and typing allows it to take both physical and special hits, and a key resistance to common Fighting-type attacks helps it immensely. Its access to Spore and Rage Powder allows it to fit into any team, and especially helps Trick Room teams to set up. However, many common Pokemon, such as Tornadus, Reuniclus, and Chandelure, can easily OHKO it, and its low Speed stat means it can't do much to stop this. Overall, though, its tremendous bulk and access to Spore makes Amoonguss an excellent choice for almost any team.
Spore, in conjunction with Amoonguss's excellent bulk, will almost always incapacitate an opponent the first turn unless they specifically prepare for it. Rage Powder allows Amoonguss to help its team set up field effects such as Tailwind or Trick Room, and with its bulk, it can easily take moves that could OHKO frailer Pokemon. It also attracts Beat Up, so the vaunted Beat Up Whimsicott-Terrakion combination utterly fails against Amoonguss. Giga Drain 2HKOes Terrakion, and does good damage to Water-types such as Jellicent or Samurott while healing back HP. It also helps break Focus Sashes. Protect allows Amoonguss to stall the opponent, and gives its partner time to take out whatever may be threatening it. The EVs give it excellent special bulk, allowing it to take Reuniclus's Life Orb Psychic and take much less damage from Chandelure's Heat Wave.Team Options & Additional Comments >>>
Amoonguss can be used at levels lower than 50, in order to outspeed more Pokemon in Trick Room with only a minor decrease in bulk. For example, at level 49, Amoonguss Speed ties with Musharna, and outspeeds opposing Reuniclus and Amoonguss in Trick Room, allowing it to become a more effective check to opposing Trick Room teams. Amoonguss has access to Synthesis, which increases its survivability even more, but it suffers from four moveslot syndrome already, and is still OHKOed by strong super effective attacks or when double-targeted. Its low Speed also means it won't be able to recover health very easily. Amoonguss has access to both Rain Dance and Sunny Day, allowing it to support a rain- or sun-based team, but it has very low Speed, making it generally inferior to Pokemon such as Whimsicott and Volcarona, who can set the weather up with priority or substantial offensive presence. Substitute can work well with Amoonguss's excellent defenses, but it has lacks the offensive stats to take advantage of it, and is generally much more effective just using Spore to incapacitate the opponent. Sludge Bomb is an alternate attacking move that has higher Base Power than Giga Drain, but does not recover health, nor does it allow Amoonguss to take out Terrakion even with Safeguard up, and as such is usually an inferior choice.
Amoonguss can be used well in Tailwind teams simply because of its access to Spore, allowing it to incapacitate the bulkier Pokemon that plague Tailwind teams. Although utilizing a Timid nature and 252 Speed EVs causes Amoonguss to lose a lot of bulk, it can outspeed all Pokemon up to Thundurus and Tornadus when Tailwind is up. Amoonguss can also run a whole host of other items to confound its usual counters. While Mental Herb and Coba Berry halt the most standard counters, an Occa Berry stops Chandelure's Fire Blast or Overheat from OHKOing, and a Yache Berry can allow it to survive a Vanilluxe's Ice Beam, giving it an extra turn to use Rage Powder or Spore an opponent. Focus Sash allows Amoonguss to survive an attack of any type, but means it will die after using Rage Powder, and is generally an inferior choice. While it doesn't stop these attacks, a Sitrus Berry greatly increases Amoonguss's survivability and allows it to tank neutral assaults much more easily, making it yet another viable choice.
Checks and Counters
Tornadus and Archeops can both do great damage to Amoonguss with a Flying Gem-boosted Acrobatics, and can KO with help from a partner, giving it no chance to support the team at all. A partner such as Terrakion utilizing super effective attacks or a Trick Room user such as Reuniclus can help tremendously, KOing the aforementioned threats with Rock Slide or setting up Trick Room as Amoonguss uses Protect. A Fire Gem-boosted Heat Wave from Chandelure also OHKOes Amoonguss, as does an unboosted Fire Blast or Overheat. Chandelure has many weaknesses, though, and with its base 80 Speed, it's not too difficult to take out; a Terrakion's Rock Slide or Landorus's Earthquake will KO it if it's not holding Focus Sash, and a bulky Trick Room user such as Musharna can set up Trick Room as Amoonguss uses Protect. Musharna, Reuniclus, and Beheeyem are Pokemon which commonly set up Trick Room, and they can all OHKO or 2HKO Amoonguss with Psychic. Escavalier can help to rectify this, outspeeding the above threats under Trick Room and KOing with X-Scissor or Megahorn. Chandelure can also help if Trick Room is not up yet, 2HKOing both with Shadow Ball, or OHKOing with a Ghost Gem-boosted Shadow Ball.
Any Taunt user can stop Amoonguss in its tracks if it doesn't have Mental Herb. Thundurus and Tornadus with Substitute are often used to stall out turns of Trick Room, and can completely obstruct any of Amoonguss's assaults if it does not possess Hidden Power Ice. A Rock Slide user such as Conkeldurr can break their Substitutes, while Gigalith can outspeed Amoonguss in Trick Room and break the Substitute with Rock Slide, allowing Amoonguss to put them to sleep with Spore. Pokemon such as Terrakion and Virizion can use Safeguard to stop Amoonguss from using Spore.