Manaphy

Manaphy is one of the undisputed strongest stallbreakers in the whole tier thanks to the combination of Tail Glow and Hydration, which makes it temporarily immune to Toxic in rain, so it naturally finds itself a place on several rain teams as their countermeasure to the stall matchup. Additionally, Manaphy is also a deadly wallbreaker with a rain-boosted +3 Hydro Vortex that makes it almost effortless to weaken typical rain checks for the likes of Mega Swampert and Ash-Greninja to clean up. With Psychic as coverage, Manaphy can also break past notable threats to rain, such as Toxapex and Mega Venusaur. Manaphy's great bulk all-around also gives it a plethora of opportunities to set up, and a Water-type resistance helps with the opposing Ash-Greninja matchup in rain. However, Manaphy's relative lack of raw power makes it somewhat predictable and exploitable, as it needs to set up with Tail Glow to actually do damage, making easier to play around than most wallbreakers. This, accompanied by the fact that nearly all teams have something to outspeed it, also makes it a bit easy to play around, as it's not hard to pivot into a faster Water-resistant threat as it sets up Tail Glow, such as Serperior or Protean Greninja, and even when Manaphy does take down a Pokemon on the opposing team, it will be likely forced out by a faster threat such as Choice Specs Tapu Koko or Kartana.