Tapu Koko

Tapu Koko has a small niche thanks to it support it setting Electric Terrain, which supports Regieleki's powerful Electric-type moves, especially Rising Voltage, and blocks sleep moves like Spore. Tapu Koko further supports Regieleki by OHKOing Rillaboom with Choice Band-boosted Brave Bird, opening up the way for Regieleki to use Rising Voltage unhindered by Grassy Terrain. Tapu Koko is only found on certain hail teams alongside teammates such as Alolan Ninetales, Kyurem-B, and Genesect that can check and threaten Grass- and Ground-types like Zygarde, Landorus, and Rillaboom with Blizzard. However, Tapu Koko heavily struggles with the prevalence of Ground- and Grass-types in DOU such as Landorus, Zygarde, and especially Rillaboom, which overrides Electric Terrain with Grassy Terrain. Furthermore, it can only be used with decent effectiveness on one niche archetype that requires another niche Pokemon in Regieleki, leaving Tapu Koko as a suboptimal pick in DOU.