Still super impressed with how customizable this thing is, there are just so many routes to go. It's definitely my favorite pokemon from this generation, both design-wise and competitively. Here's a basic framework:
Tapu Koko@Life Orb
Naive; 4 Atk / 252 SpA / 252 Spe
Electric Surge
Thunderbolt / Wild Charge
HP Ice / Grass Knot
Brave Bird / Dazzling Gleam
U-turn / Calm Mind / Work Up
Naive nature and Life Orb I think will be mandatory, though there is a case for Expert Belt or Zap Plate. You can literally do no wrong as the only thing KoKo needs is electric STAB - cool features follow:
- Thunderbolt is preferable here due to the lack of recoil and perfect accuracy. It has a 68% chance to 2HKO SpD Heatran after rocks and leftovers, which is quite a feat for a neutral move and gives you an idea of its power.
- Wild Charge with 184 Atk EVs (a commitment to a physical slant and possibly Work-Up, I know) does cool things like OHKO SpD Heatran, SpD Jirachi, and BandTar at +1. It would best be used in conjunction with Brave Bird to hit the bulky grasses that shut this down.
- HP Ice is good coverage for Lando-T, Gliscor, and Garchomp - it only requires 44 SpA EVs at +1 for the OHKO and obviously cleanly 2HKOs otherwise.
- Grass Knot is notable for hits on Mixed wall Hippowdon, Unaware Quagsire, and Mega Swampert if you're worried about those.
- Brave Bird is really only notable alongside Wild Charge for coverage on Amoonguss / AV Tangrowth / Def Mega Venusaur, all of which it is capable of OHKOing at +1 with Stealth Rock. It also picks up KOs on weaker pokemon such as 4/0 Latios.
- Dazzling Gleam is Tapu Koko's only Fairy coverage but it gets the job done. With maximum investment and a +1 boost, it can OHKO 252 HP Latias with Stealth Rock, likely the most specially defensive Dragon to be found in OU.
- U-turn provides excellent utility on any pokemon and is particularly solid on a speedster like Tapu Koko. I think it will be preferable to Volt Switch as it doesn't have any immunities and also hits notable targets in the Lati twins and various grass-types.
- The last two moves provide boosting opportunities. Calm Mind allows moves like Grass Knot and DGleam the power to OHKO their targets. Work Up is an option for any mixed set that utilizes a physical attack.
Thanks to it's coverage and speed, Tapu Koko's main obstacles in OU are limited to Excadrill, Ferrothorn, and Magnezone. It has some way around nearly every other pokemon in the tier. It can always forgo some of this coverage for utility options in Roost and Taunt.