What this set has over the other sets: beating mons that usually beat the other sets such as the pink blobs
What the other sets have over this set: abiliity to bring team support to the table by pivoting teammates in and maintain momentum via switch moves. Able to threaten fierce offensive threats such as manaphy and unevolved ash greninja.
Unaware Clefable
0 SpA Unaware Clefable Moonblast vs. 252 HP / 0 SpD Tapu Koko: 124-147 (36 - 42.7%) -- 96% chance to 3HKO after Leftovers recovery
+1 0 SpA Tapu Koko Dazzling Gleam vs. 252 HP / 0 SpD Unaware Clefable: 91-108 (23 - 27.4%) -- possible 5HKO after Leftovers recovery
Probably the first thing that comes to mind that could beat this set without properly beating the other sets. Usually only seen on stall teams. You taunt it and basically roost while gaining enough calm minds to barrage through the rest of the stall team.
There will be some sticky situations where koko is forced to either roost, attack or taunt again but it's still winnable if played well.
Heatran /
252+ SpA Heatran Inferno Overdrive (180 BP) vs. +2 252 HP / 0 SpD Tapu Koko: 205-243 (59.5 - 70.6%) -- guaranteed 2HKO
252+ SpA Heatran Earth Power vs. +2 252 HP / 0 SpD Tapu Koko: 138-164 (40.1 - 47.6%) -- guaranteed 3HKO
0 SpA Heatran Earth Power vs. 252 HP / 0 SpD Tapu Koko: 206-244 (59.8 - 70.9%) -- guaranteed 2HKO
0 SpA Heatran Earth Power vs. +1 252 HP / 0 SpD Tapu Koko: 138-164 (40.1 - 47.6%) -- guaranteed 3HKO
+6 0 SpA Tapu Koko Dazzling Gleam vs. 252 HP / 136+ SpD Heatran: 62-73 (16 - 18.9%) -- possible 8HKO after Leftovers recovery
Strongest hit from heatran possible won't kill, so offensive heatran can only win when it's a 1v1 whereas if heatran have revealed leftovers then it would likely to be defensive and koko can just setup safely while potentially even pp stalling defensive heatran by itself without it being a 1v1 ofc since koko has to taunt to prevent the taunt from heatran itself or even a rare but respected possibility of toxic.
Charizard-Y
252 SpA Charizard-Mega-Y Fire Blast vs. +2 252 HP / 0 SpD Tapu Koko in Sun: 199-235 (57.8 - 68.3%) -- guaranteed 2HKO after Leftovers recovery
+6 0 SpA Tapu Koko Dazzling Gleam vs. 0 HP / 0 SpD Charizard-Mega-Y: 146-172 (49.1 - 57.9%) -- 97.7% chance to 2HKO
Ironically you need to stall out sun turns, and it's still a little bit risky with the rolls, however it's the same case as the pyukumuku and quagsire situation mentioned above, it's super risky for them to just throw in zard y without confirming the set. And by the time they do so the team will likely to be in battered shape. Or if luck is on your side and you managed to stall out sun turns then you will be able to
Blissey And Chansey /
+6 0 SpA Tapu Koko Dazzling Gleam vs. 252 HP / 4 SpD Blissey: 253-298 (35.4 - 41.7%) -- guaranteed 3HKO
+6 0 SpA Tapu Koko Dazzling Gleam vs. 248 HP / 8 SpD Eviolite Chansey: 210-247 (29.8 - 35.1%) -- 18.7% chance to 3HKO
The Pink blobs can't really do anything except spam seismic toss or teleport because of taunt, so koko will get to +6 eventually and run through them.
Magnezone /
252+ SpA Choice Specs Magnezone Flash Cannon vs. +1 252 HP / 0 SpD Tapu Koko: 183-216 (53.1 - 62.7%) -- guaranteed 2HKO after Leftovers recovery
252+ SpA Choice Specs Magnezone Flash Cannon vs. +2 252 HP / 0 SpD Tapu Koko: 136-162 (39.5 - 47%) -- guaranteed 3HKO after Leftovers recovery
252+ SpA Magnezone Corkscrew Crash (200 BP) vs. +2 252 HP / 0 SpD Tapu Koko: 228-268 (66.2 - 77.9%) -- guaranteed 2HKO
252+ SpA Magnezone Steel Beam vs. +2 252 HP / 0 SpD Tapu Koko: 160-189 (46.5 - 54.9%) -- 62.1% chance to 2HKO
Although zone is not really a so called reliably counterplay against koko since it doesn't block volt switch, it's decent at staving it off temporarily due to resisting all of it's hits after it's done trapping/nothing to trap at. Koko can beat both sets if zone comes in after it threatens a switch while having a chance of defeating the specs set 1 on 1
(i'm not gonna calculate that since i'm lazy and suck).
Amoonguss /
0 SpA Amoonguss Sludge Bomb vs. +2 252 HP / 0 SpD Tapu Koko: 108-128 (31.3 - 37.2%) -- 78.6% chance to 3HKO
+6 0 SpA Choice Specs Tapu Koko Dazzling Gleam vs. 248 HP / 204 SpD Amoonguss: 235-277 (54.5 - 64.2%) -- guaranteed 2HKO after Black Sludge recovery
Electric terrain means that we are temporarily shielded from spore for enough time and we don't need to taunt for the time being since toxic is incredibly rare and slotting it in on the mushroom has some issues on its own right. Sludge Bomb poison is gonna be annoying but there's nothing we can really do about it. This might make you think of av tang but no CM koko doesn't beat av tang as it could fish for sludge bomb poison and spam power whip as it forced to roost or just eq the guardian of alola.