Rage Powder is a necessity for all Amoonguss sets and allows moves to be redirected towards its bulky self.

Spore puts foes to sleep, which renders them temporarily useless. Due to Amoonguss's low speed, it severely punishes threats in Trick Room this way before they can act.

Clear Smog does decent damage and also resets opposing Pokemon's stat changes to zero. This should be used against Belly Drum Snorlax or Competitive Milotic.

Sludge Bomb chunks both Grass- and Fairy-types such as Ludicolo, the Tapu group, and Gardevoir.

Giga Drain allows Amoonguss to recover health whilst doing solid damage. It also deals large chunks of damage to Milotic and Mega Swampert.

Protect is a staple move in VGC and should be used to scout out for moves, defend Amoonguss, or allow an ally to remove a threat.

The EVs combined with a Sassy nature allow Amoonguss to survive a sun-boosted Heat Wave from Mega Charizard Y and guarantees Landorus-T's Earthquake to deal less than 50% of damage.

Wiki Berry maximizes recovery. However, if you do not want to risk it not being activated, you can go with a Sitrus Berry.

An alternative, more physically bulky option to go with is available with a Relaxed nature and an EV spread of 244 HP / 196 Def / 68 SpD. These can be used to survive a non-Terrain-boosted Zen Headbutt from Mega Metagross.

Tapu Koko and Tapu Fini are minor threats to Amoonguss, as their Terrains make Spore unusable against grounded Pokemon. However, Amoonguss does decent damage to Tapu Fini with both Sludge Bomb and Giga Drain, and it can redirect Electric-type moves from Tapu Koko and easily take them.

Amoonguss forms a nice duo with Mega Kangaskhan and Tyranitar to defend them against incoming Fighting-type moves they are weak to. In addition to this, Tyranitar can safely set up with Dragon Dance with the assistance of redirection from Amoonguss.

Amoonguss is a good lead, as it can be immediately threatening, and you shouldn't be overly concerned about it taking damage early-game, because its recovery tools will allow it to continue supporting its teammates late-game. You don't want to focus too much on recovery, because it is not very good if it remains as your last Pokemon. Sometimes sacrificing Amoonguss is alright if it saves its partner from a strong hit in doing so.