Been looking forward to doing Nidoking. I personally love using him in the rain, just for Thunder's increased power. Let's take a look.
Nidoking (M) @ Life Orb
Trait: Sheer Force
EVs: 4 HP / 252 SAtk / 252 Spd
Timid Nature (+Spd, -Atk)
- Surf / Ice Beam
- Earth Power
- Sludge Wave
So he's still basically his same awesome self; just with a few new tricks.
Thunder gets even better boosted power than Thunderbolt does. Earth Power is STAB. Sludge wave is STAB. Ice Beam gives bolt-beam combo and has no Life orb damage, or you can run Surf and take a little bit of Life orb damage, but have Rain boosted power ( but not sheer force boosted ).
Nidoking (M) @ Leftovers / Wide Lens
Trait: Poison Point
EVs: 252 HP / 252 Atk / 4 SDef
Adamant Nature (+Atk, -SAtk)
- Aqua Tail
- Dragon Tail
- Stealth Rock
If you're feeling creative. I recommend baton passing defense boosts to this guy for extra awesomeness.
Megahorn is great coverage. Aqua Tail is rain boosted and acts as his STAB. Dragon Tail phases. Stealth Rock sets up.
Good tank if you can baton pass defenses. I prefer the first set.
Overall, just use him the way you would use him outside of the rain, with tricks like Thunder tacked on. And you'll get good use out of him.
Rating for the rain -- 6/10