Decidueye

Ghost

Decidueye is a good defensive option on Ghost teams thanks to its access to effective utility moves. Its Grass typing and solid Special Defense allow it to switch into Ground- and Electric-types such as Landorus, Seismitoad, Tapu Koko, and Alolan Raichu. It is also the only viable Ghost-type with access to Defog, which allows it to remove entry hazards such as Stealth Rock and Toxic Spikes, which would otherwise weaken Ghost's defensive core. With Spirit Shackle, Decidueye is able to trap defensive Pokemon that Ghost has difficulty dealing with like Mega Venusaur, Baneful Bunker Toxapex, and Clefable and eventually beat them after setting up with Swords Dance. However, Decidueye's Attack stat is incredibly mediocre without any boosts, leaving it unable to do any serious damage against offensive threats, and it's unable to hit Normal-types at all due to only running Spirit Shackle. Its lacking Speed stat also means that it can only check slow defensive Pokemon, and its low Defense makes it unable to switch into physical attacks from offensive Pokemon like Mega Diancie or Tapu Bulu. Decidueye also is extremely vulnerable to a plethora of defensive Pokemon, such as Mega Sableye, Alolan Muk, and Skarmory.

Grass

Decidueye's access to Swords Dance along with its decent Attack and Ghost-type STAB moves allows it to serve as a setup sweeper on Grass teams. Its STAB Spirit Shackle allows it to turn the tide against Psychic teams, a normally hard matchup for Grass teams to handle. Spirit Shackle is also extremely useful for trapping, which helps Decidueye reliably pick Pokemon off with its Z-Move or set up with Swords Dance. Its powerful Z-Move in Sinister Arrow Raid allows it to KO bulky targets such as Toxapex, Celesteela, Zapdos, and Ferrothorn when boosted and further supports its sweep. Grass teams also appreciate Decidueye's ability to keep up entry hazards by acting as a spinblocker through its Ghost typing. However, Decidueye's limited bulk thins the number of setup opportunities it gets and forces it to set up against weaker Pokemon or late-game. Decidueye's underwhelming Speed stat also leaves it outsped by common offensive threats such as Heatran and forces it to rely on priority attacks such as Shadow Sneak to pick off faster threats.