Scenarios if hydro hit:
hydro does 252 SpA Keldeo Hydro Pump vs. 0 HP / 0 SpD Mimikyu: 172-204 (68.5 - 81.2%) -- guaranteed 2HKO
mimikyu takes me out with +4 sneak, after LO damage, has 9-21% hp left

Scenario 1:
I go mmaw, click sucker and he spectrals. In this scenario, hes just fucked up and I win very easily because mmaw espeed does: 252+ Atk Huge Power Mawile-Mega Extreme Speed vs. 0 HP / 0 Def Diancie-Mega: 76-89 (31.5 - 36.9%) -- 79.9% chance to 3HKO, and awak sneak does: 252+ Atk Thick Club Marowak-Alola Shadow Sneak vs. 0 HP / 0 Def Diancie-Mega: 96-114 (39.8 - 47.3%) -- guaranteed 3HKO. SO following these 2 attacks, mdiancie is at 28-23%, and if it quiver danced, it lost to sneak. if it killed both, then its vs fini at +0, and fini just scalds and wins.

Scenario 2:
I go mmaw, he sneaks on the sucker punch and does: +3 252+ Atk Life Orb Mimikyu Shadow Sneak vs. 252 HP / 0 Def Mawile-Mega: 149-177 (49 - 58.2%) -- 98% chance to 2HKO. Now, depending on the hydro roll, hes either dead, or at 1-11% hp. If he is dead, then its game over again, if hes alive then we split into 2 possible scenarios:

Scenario 2a:
he sneaks again on my sucker punch, and either dies, or lives on 1% if hydro min rolls. If he lives on 1%, then probably (barring a missplay) wins the match barring a scald crit on diancie, however this only happens if he gets an absolute min-roll on hydro. If he does miraculously gete a min roll, he then kills awak, and its fini vs mdiancie with rocks up on my side. fini is at 88%, and moonblast does a max of 46% if modest. this does not 2kho, while scald does. IF he quiver dances, then he most likely wins, unless i get 2 max rolls with scald: 0 SpA Tapu Fini Scald vs. +1 0 HP / 0 SpD Diancie-Mega: 102-122 (42.3 - 50.6%) -- 2% chance to 2HKO. IF however he dies to LO, he most likely takes out mmaw (barring 2 min rolls) but he still loses. This is because its mdiancie vs fini and awak. IF he earthpowers the awak, he takes 40-47% from sneak, and then dies to scald, as he has no means of taking fini out in 1 turn. IF he quiver dances on the awak, then he also loses, because sneak 3kho's, so wak would be able to sneak twice, putting diancie within scald range even at +1 spd, and mdiancie DOES NOT OKHO fini at +1 spa.+1 252 SpA Diancie-Mega Moonblast vs. 248 HP / 96+ SpD Tapu Fini: 183-216 (53.3 - 62.9%) -- guaranteed 2HKO after Leftovers recovery

Scenario 2b: He switches out on the second sucker punch (I was always gonna sucker twice). In this scenario, he has his mdiancie vs my mmaw. Also, his mimikyu is at 1-11%hp. I espeed the mdiancie, doing 32-37%, he either earth powers killing mmaw, or he qd's. IF he qd's he loses, and if he earth powers he also loses. IF he qd's, i get off 2 espeeds, doing 64-74%, and then one shadow sneak from awak kills mdiancie, leaving the mimikyu which fini handily takes care of. IF he earthpowers, I still go awak and sneak, leaving him at 28-23% which is within a scald from fini, and mimikyu does nothing to fini without any boosts. 252+ Atk Life Orb Mimikyu Spectral Thief vs. 248 HP / 192 Def Tapu Fini: 122-146 (35.5 - 42.5%) -- 93.5% chance to 3HKO after Leftovers recovery, 252+ SpA Diancie-Mega Moonblast vs. 248 HP / 96+ SpD Tapu Fini: 135-159 (39.3 - 46.3%) -- guaranteed 3HKO after Leftovers recovery

There are no other feasible scenarios if hydro had hit, and therefore if hydro did hit i can say with certainty that I won, unless I minrolled hydro, and I didnt max roll twice with scald in the following circumstances explained above. This is barring any crits, as crits would of course change up a lot of stuff, but they are just further hax, and this is predicting what woulda happened in a haxless game.