>>17309145252+ SpA Life Orb Sheer Force Nidoking Earth Power vs. 252 HP / 4 SpD Mega Mawile: 424-502 (139.4 - 165.1%) -- guaranteed OHKO
252+ SpA Life Orb Sheer Force Nidoking Sludge Wave vs. 252 HP / 252+ SpD Togekiss: 283-338 (75.6 - 90.3%) -- guaranteed 2HKO after Leftovers recovery
252+ SpA Life Orb Sheer Force Nidoking Earth Power vs. 252 HP / 0 SpD Klefki: 463-546 (145.5 - 171.6%) -- guaranteed OHKO
252+ SpA Life Orb Sheer Force Nidoking Sludge Wave vs. 252 HP / 4 SpD Azumarill: 517-611 (127.9 - 151.2%) -- guaranteed OHKO
252+ SpA Life Orb Sheer Force Nidoking Sludge Wave vs. 252 HP / 252+ SpD Sylveon: 260-307 (65.9 - 77.9%) -- guaranteed 2HKO after Leftovers recovery
This is all before rocks, and those are the most viable fairy types. The most threatening response to the king is Azumarill, who's water typing does pose a threat. However, Nidoking does outspeed him by default, and this is how Azumarill responds in a 1 on 1 situation:
252+ Atk Huge Power Azumarill Aqua Jet vs. 4 HP / 0 Def Nidoking: 200-236 (65.7 - 77.6%) -- guaranteed 2HKO
Pretty fucking strong. Keep rocks up and your opponent has problems, as Nidokings 2HKOs quickly turn into OHKOs.