Nidoking (RR) is one of the techs that Rising Rivals came up with but Nidoqueen (RR) is miles ahead of it in terms of being a playable tech. And there are several reasons why.
But first off, the basics of the card. HP of 130 is great for Stage 2's, weakness to water is bad due to Palkia G, Kingdra, and Gyarados around, resistance is great against Luxray GL, and 2 retreat cost is quite unexpected for something as big as Nidoking but is very much appreciated.
Territoriality is somewhat an offensive Poke-Body compared to the defensive Maternal Comfort. Racking up 2 extra damage counters per turn is nice and can easily add up. It can be made better use of by having an active Pokemon that can take several hits, for more passive damage. Effects do get around the body but not many place damage counters anymore when attacking due to the prevalence of Unown G (except for Gengar SF).
Fling Away si somewhat overcosted for a Stage 2, doing a total of 60 damage (direct or with snipe). However, if you accumulated enough counters with Territoriality, the snipe can be of help. Sadly, Kingdra LA can do the same total damage with only 1 Energy and a discard.
Giant Horn is a flippy attack to do 100 damage for 4 (at least only 3 colorless energy are required). Although there's a relatively low chance that the attack fails (about 25%), it's still annoying when you get both tails during crucial moments, especially for what seems to be Nidoking's main attack. Theoretically , Shiftry RR destroys the attack's usefulness, but Shiftry is not really played. Four energies is a bit steep but there are ways to reduce energy requirements, either using Nidoqueen MT or the using the less reliable Upper Energy.
Even if the Poke-Body is great, its attacks are somewhat lackluster- the reason why Nidoqueen is better. Mega Punch and Ruthless Tail are more reliable attacks and Nidoqueen can become quite an attacker in a pinch. Because of this, Nidoking is relegated to the tech status and nothing more (except for the Monarchy deck). It is a nice tech but others clearly outshine it as one (Nidoqueen, Dusknoir, Exploud, to name a few). It seems that it can fit in a lot of decks but most do not have space for it, it does not really gel well with particular strategies, nor it can help with particular match-ups the way other techs do. It has a lot of potential but pretty much regarded as a less useful option.
Modified- 6/10 (nice Poke-Body but the attacks could have been better. Other techs are better)
Limited- 9/10 (Territoriality is a killer here if you manage to get the full line out)
