Azumarill

Azumarill is a strong Pokemon despite a mediocre-looking base 50 Attack stat, as with its access to Huge Power, Azumarill becomes a threatening attacker. Thanks to its decent defensive stats and Water / Fairy typing, Azumarill has plenty of opportunities to set up with Belly Drum and sweep with Aqua Jet, making Azumarill a threatening offensive wincon in Doubles OU that can make quick work of teams that are weakened or unprepared for it. Azumarill is let down by its poor Speed, however, though this can be an asset with the use of Trick Room. This makes Azumarill rely on Aqua Jet to KO faster Pokemon, which is not reliable because of Tapu Lele's Psychic Terrain. While Azumarill does have good bulk that allows it to use Belly Drum in a variety of situations, it typically needs support in the form of redirection or Fake Out in order to create a situation in which it can sweep the opposing team. Azumarill is also able to be worn down by Intimidate and burns, which can quickly reduce its ability to threaten a team. Additionally, sharing a typing with a metagame threat as common as Tapu Fini leads to most teams being naturally prepared for Azumarill, despite its own rarity.