+1 176 SpA Nihilego Meteor Beam vs. 0 HP / 4 SpD Alakazam: 285-336 (113.5 - 133.8%) -- guaranteed OHKO
+1 176 SpA Nihilego Meteor Beam vs. 0 HP / 0 SpD Azelf: 366-432 (125.7 - 148.4%) -- guaranteed OHKO
+1 176 SpA Nihilego Meteor Beam vs. 0 HP / 4 SpD Azumarill: 328-387 (96.1 - 113.4%) -- 75% chance to OHKO
+1 176 SpA Nihilego Meteor Beam vs. 0 HP / 4 SpD Crawdaunt: 439-517 (164.4 - 193.6%) -- guaranteed OHKO
+1 176 SpA Nihilego Meteor Beam vs. 0 HP / 4 SpD Gyarados: 546-644 (164.9 - 194.5%) -- guaranteed OHKO
+1 176 SpA Nihilego Meteor Beam vs. 56 HP / 0 SpD Kyurem: 596-704 (147.1 - 173.8%) -- guaranteed OHKO
+1 176 SpA Nihilego Meteor Beam vs. 0 HP / 4 SpD Lycanroc-Dusk: 387-456 (132.9 - 156.7%) -- guaranteed OHKO
+1 176 SpA Nihilego Meteor Beam vs. 0 HP / 4 SpD Mamoswine: 411-484 (113.8 - 134%) -- guaranteed OHKO
+1 176 SpA Nihilego Meteor Beam vs. 0 HP / 4 SpD Moltres-Galar: 450-530 (140.1 - 165.1%) -- guaranteed OHKO
+1 176 SpA Nihilego Meteor Beam vs. 248 HP / 0 SpD Ninetales-Alola: 546-644 (156.4 - 184.5%) -- guaranteed OHKO
+1 176 SpA Nihilego Meteor Beam vs. 248 HP / 92+ SpD Rotom-Heat: 432-510 (142.5 - 168.3%) -- guaranteed OHKO
+1 176 SpA Nihilego Meteor Beam vs. 0 HP / 4 SpD Salamence: 656-774 (198.1 - 233.8%) -- guaranteed OHKO
+1 176 SpA Nihilego Meteor Beam vs. 0 HP / 4 SpD Scizor: 328-387 (116.7 - 137.7%) -- guaranteed OHKO
+1 176 SpA Nihilego Meteor Beam vs. 252 HP / 0 SpD Skarmory: 366-432 (109.5 - 129.3%) -- guaranteed OHKO
+1 176 SpA Nihilego Meteor Beam vs. 252 HP / 4 SpD Tangrowth: 471-555 (116.5 - 137.3%) -- guaranteed OHKO
+1 176 SpA Nihilego Meteor Beam vs. 0 HP / 4 SpD Tapu Bulu: 285-336 (101.4 - 119.5%) -- guaranteed OHKO
+1 176 SpA Nihilego Meteor Beam vs. 0 HP / 4 SpD Victini: 546-644 (160.1 - 188.8%) -- guaranteed OHKO
+1 176 SpA Nihilego Meteor Beam vs. 0 HP / 4 SpD Zeraora: 328-387 (103.4 - 122%) -- guaranteed OHKO
So total 18 Pokemon.
Source
I have done calculation with all UU Pokemon, but listed those who get KOed only.
Hope this helps.