Nidoking is the quintessential blue-collar Pokemon. It evolves from one of the earliest Pokemon you encounter in RBY, its stats aren't flashy—the best it gets is base 92 Attack—and its typing is a strange Poison / Ground mixture that you wouldn't expect to be great defensively. Regardless of these reasons for humility, Nidoking has all the right tools to get the job done as the premier mixed attacker of GSC. For starters, its movepool gives it a fairly strong STAB Earthquake coupled with solid super effective coverage moves for physical walls and Pokemon that resist it. Nidoking's immunities to Toxic and Thunder and its base 85 Speed, which is particularly fast by GSC standards, are also nice advantages that Nidoking totes over other attacking threats. However, that's not all Nidoking has to offer, for if that were the case, it would still be outclassed by Pokemon with flashier stat spreads such as Tyranitar and Dragonite. Access to Lovely Kiss is Nidoking's ace in the hole, allowing it to instantly take one of its chief counters out of the game, something the other mixed sweepers can't do.
This set allows Nidoking to threaten as wide an array of opponents as possible. STAB Earthquake running off a decent Attack stat is Nidoking's main attacking move, and it does solid damage to most threats. However, it does run short of hitting relevant KO thresholds against certain walls, such as Snorlax, Miltank, and Umbreon; Earthquake will shave off roughly 25-30% of these threats' HP, which is well short of a 3HKO and just short of even a 4HKO after Leftovers. That's where Lovely Kiss comes in. With a well-timed Lovely Kiss, one of these walls can be indefinitely incapacitated, allowing Nidoking to go for the KO itself by spamming Earthquake or permitting a teammate to switch in and start setting up. As for the other two moves, these are for hitting foes that resist or are immune to Earthquake for super effective damage. Ice Beam is a must to 3HKO Zapdos, as otherwise Nidoking cannot touch it even with Lovely Kiss since most Zapdos run Sleep Talk. Ice Beam also allows Nidoking to 3HKO Exeggutor and, when all else fails, to play for the freeze against Miltank. The last moveslot is a bit more flexible, although Thunder is the preferred option because it guarantees a 2HKO against Starmie and Skarmory, can 3HKO Suicune and Vaporeon, and has a 21% paralysis chance, factoring accuracy, to facilitate these KOs. However, Thunderbolt is an option if you don't want to chance a miss against a Cloyster, Skarmory, or weakened Suicune in KO range. That said, Nidoking will miss out on the KO thresholds that Thunder achieves, and furthermore it will do more damage to Vaporeon with Earthquake than it would with Thunderbolt.Team Options & Additional Comments >>>
Fire Blast is an attacking option that allows Nidoking to cleanly 2HKO Steelix and Exeggutor while granting it an OHKO against Forretress and a 3HKO against Heracross. However, Fire Blast must go over either Ice Beam, which leaves Nidoking unable to touch Zapdos, or Thunder/Thunderbolt, which leaves Nidoking unable to do as much damage to Water-types, especially Suicune. Using Fire Blast over Thunder/Thunderbolt also makes Nidoking unable to significantly damage Charizard, which, while uncommon, can then threaten to set up Belly Drum and sweep. Counter is an interesting option for surprise KOs. Morning Sun can be used to allow Nidoking to last longer and heal off potential Hidden Powers from Zapdos and Raikou, but it cannot be used with Lovely Kiss. Counter even works against special Hidden Powers in GSC, so it allows Nidoking to bounce back Hidden Powers from Zapdos for major damage, in addition to attacks from Snorlax and Miltank. However, Counter requires careful use to ensure the opponent is definitely in KO range before it is revealed, and ultimately makes Nidoking less effective as a mixed attacker by taking away one of its attacking moveslots.
Checks and Counters
RestTalk Suicune, Heracross, and Snorlax are probably the most complete Nidoking counters in existence. All three of these Pokemon can absorb Lovely Kiss and can tank whatever attacks Nidoking can use. Suicune must watch out for the 3HKO from the inaccurate Thunder, Heracross must watch out for the rare Fire Blast 3HKO, and Snorlax, being slower than Nidoking and taking more from Earthquake than the other two counters, must be wary of switching in, especially with Spikes down. Zapdos is also a fine switch-in to Nidoking, although Ice Beam is very common, averages a 3HKO against Zapdos, and, unlike Thunder against Suicune, is 100% accurate. However, unlike the other counters, Zapdos is guaranteed to outspeed Nidoking, is immune to Earthquake and Spikes, and can 3HKO Nidoking with a super effective Hidden Power.
When Nidoking has used Lovely Kiss, many more options for countering it open up. Suicune and Snorlax without RestTalk can switch in to sponge hits and scare it out. Miltank is a fantastic switch-in when Sleep Clause is active, as Nidoking is slower and cannot penetrate its defenses with its attacks. Miltank can also force Nidoking to switch out with the threat of Body Slam paralysis. However, if Sleep Clause is not active, Miltank balks at the prospect of being put to sleep, since it is then unable to cure its teammates of status with Heal Bell. Starmie is also a solid check that outspeeds Nidoking, gets Recover to shrug off its attacks, and 2HKOes it in return. Starmie is also often common sleep bait to offer against Nidoking on teams without a Sleep Talk user. However, Starmie is 2HKOed by Thunder. Umbreon is slower than Nidoking, which makes switching into Earthquakes difficult at times, but otherwise it is a stellar wall that avoids even being 4HKOed by any of Nidoking's attacks. Umbreon, however, does struggle to threaten Nidoking in return; it can pass Mean Look to another counter that can threaten to KO Nidoking, or it can use Charm to weaken Nidoking's Earthquake to allow an easier switch to another counter.
Aside from the checks listed above, Sleep Talk Vaporeon also makes a somewhat decent answer to Nidoking. It is slower than Nidoking, is 4HKOed by Earthquake unlike Umbreon and Snorlax, and is even 3HKOed by Thunder, so it is, admittedly, a very shaky check. However, it can absorb Lovely Kiss with a Sleep Talk set and can threaten to 2HKO Nidoking in return. Other slower Pokemon that can nonetheless threaten Nidoking include Quagsire and Porygon2. Unlike Vaporeon, these Pokemon cannot absorb Lovely Kiss, but on the other hand, they are not 3HKOed by any of Nidoking's moves, either. Quagsire gets to guarantee a 2HKO in return with Earthquake, whereas Porygon2 gets access to Recover instead of relying on Rest to stay healthy.
Other slower Pokemon that struggle to switch into or threaten Nidoking are Forretress and even Blissey. Forretress generally does not have a good way to threaten Nidoking and fears the possible Fire Blast, but otherwise tanks Nidoking with ease and can even attempt to stall it out if it runs the uncommon Rest. Obviously, it wants to switch in only after Nidoking has used Lovely Kiss so that it is not rendered unable to lay Spikes. Blissey, on the other hand, is generally a cleric and so obviously wants to avoid taking a Lovely Kiss, but otherwise avoids being 2HKOed by Earthquake, which permits the use of Softboiled to attempt to stall Nidoking. In addition, Ice Beam can threaten to 3HKO Nidoking while Growl and even the odd Reflect (which cannot be used along with Heal Bell) can make tanking Earthquakes a lot easier.