Tapu Koko

Electric

Tapu Koko is Electric's most essential Pokemon due to its ability Electric Surge, providing all teammates with a boost to their Electric-type STAB attacks. Its part Fairy typing along with Dazzling Gleam is also incredibly useful to deal with Dragon- and Dark-types such as Latias, Latios, Hydreigon, and Urshifu-S, which would otherwise be difficult to beat for Electric teams. A stellar Speed tier also allows Tapu Koko to outspeed the likes of Cinderace, Tapu Lele, Choice Band Victini, and Urshifu-S, helping it set Electric Terrain and wallbreak easier. Another benefit from Electric Terrain is that grounded Pokemon cannot fall asleep; this prevents foes like Amoonguss from putting Tapu Koko and its teammates to sleep with Spore. However, Tapu Koko can be outsped by many Choice Scarf users such as Weavile, Blacephalon, and Excadrill and other faster Pokemon like Dragapult, Barraskewda, and Kingdra under rain. This forces it to take massive damage from them or switch out. Its mediocre bulk also leaves it vulnerable to priority moves and unable to consistently switch into powerful attacks, making it easily pressured during a match.

Fairy

Good coverage in Thunderbolt + Grass Knot + Dazzling Gleam allows Tapu Koko to serve as a good answer to Flying and Water teams while putting work in other matchups such as Dark, Ground, and Psychic. Electric Surge-boosted Thunderbolt is particularly useful for taking down a huge threat to Fairy teams in Celesteela, which would be problematic to deal with otherwise. A high Speed stat ensures Tapu Koko outspeeds a majority of the unboosted metagame, which means it's only revenge killed by Choice Scarf users like Dracovish, Rotom-W, and Landorus-T or a handful of naturally faster Pokemon like Barraskewda and Dragapult. However, Tapu Koko's terrible bulk makes it unable to switch into Pokemon like Celesteela and prone to getting revenge killed by priority attacks like Urshifu-R's Aqua Jet and Dragonite's Extreme Speed. Tapu Koko faces a lot of overlap on Fairy teams, as they can typically deal with Flying and Water teams, so Tapu Koko can be rather hard to justify over Pokemon like Togekiss or Alolan Ninetales. Tapu Koko is also stopped by many Pokemon such as Ferrothorn, Tapu Bulu, and Excadrill, which makes it hard for it to make progress in certain matchups.