Diancie

Diancie shines as one of the best Trick Room setters and beneficiaries due to its high offensive and defensive stats, low Speed, strong typing, and access to Diamond Storm, fitting the unique role of a reliable Trick Room setter that can also deal out massive damage. Offensively, Rock has minimal resistances and hits common Pokemon like Kyurem-B and Incineroar super effectively. While its typing might leave it with four common weaknesses, its outstanding defensive stats mean that it can usually take a hit and activate Weakness Policy. Diancie fits best on semi-Trick Room compositions, where it takes advantage of its low Speed and can set up Trick Room multiple times and start shredding holes in the opponent's team with Diamond Storm, stacking Defense boosts to make it much harder to get rid of. Clear Body also lets it ignore Intimidate, making it very hard to stop once it gets going. Volcanion makes for an excellent partner, as it helps remove Grass- and Steel-types such as Rillaboom and Genesect for Diancie, which in return provides reliable speed control. Rillaboom's Fake Out makes Trick Room easier to set up and its powerful Grass-type STAB moves help against Urshifu-R and Tapu Fini. In return, Diancie takes care of Fire-types and Kyurem-B. Diancie struggles quite a bit outside of Trick Room, where its poor Speed leaves it vulnerable to super effective hits from the likes of Urshifu-R, Rillaboom, Zygarde, and Genesect, the first ignoring any Defense boosts Diancie might accumulate and the second having strong priority to hit first even if Trick Room is active. Diancie is also hard walled by Metagross, and must always worry about its strong Steel-type STAB moves threatening an OHKO. Furthermore, it can struggle to break past bulkier Pokemon such as Tapu Fini and Amoonguss even under Trick Room, the latter of which is able to land Spore freely if Diancie isn't using Safety Goggles.