The Nidos
You needn't Nidoking and Nidoqueen on the same team. You should choose the one you like better. Nidoking boast greater offensive stats and higher speed while Nidoqueen is bulkier.
I prefer Nidoking but both are fine, just not together.
Nidoking, although having a great attack stat, is much better pulling off a special-attacking set.
Nidoking @ Assault Vest / Choice Scarf / Life Orb:
Trait: Sheer Force
EVs: 252 SpA / 252 Spe / 4 SpD
Timid / Modest Nature
- Earth Power / Stealth Rock
- Sludge Bomb / Sludge Wave
- Ice Beam / Flamethrower
- Thunderbolt / Flamethrower / Earth Power
The nice thing about Nidoking is, it's far from being restrictive.
Item choice is determinant. With the former, you win bulk; this goes at expense of some power. The second, Choice Scarf, gives your Nidoking needed speed to run Modest more comfortable without worrying about being outsped. With Life Orb, you can freely set rocks, switch between the moves and have extra power; this however goes at the expense of durability.
The first move should be Earth Power; if you decide to run Life Orb, you may chose Stealth Rock instead and lead with Nidoking. Sludge Bomb is needed STAB; I prefer it to Sludge Wave because of better chance to poison although the latter is slightly stronger. Ice Beam and Thunderbolt go on a great tandem together and are known under the BoltBeam name. This combination allows almost full neutrality on the game, meaning that very rarely you'll see a Pokemon that resist both Ice Beam and Thunderbolt. Flamethrower is a decent alternative to any of the two if you like using it against Bug- and Ice-type Pokemon but don't run it with Life Orb and Stealth Rock because the latter beat the other types while Sludge Bomb and Earth Power beat the rest of what Fire can cover for Nidoking.
Nidoqueen can run a similar-looking moveset, although she will hit weaker but last longer.
Since you ought to drop one of the two Nido, use Crobat. He is an excellent member to Mono-Poison, steamrolling Mono-Fighting and severely denting neutral types because of its natural great attack stat.
Crobat @ Life Orb / Focus Sash:
Trait: Infiltrator
EVs: 252 SpA / 252 Spe / 4 SpD
Timid / Modest Nature
- Nasty Plot
- Heat Wave
- Air Slash
- Sludge Bomb
OR
Crobat @ Life Orb:
Trait: Infiltrator
EVs: 252 Atk / 252 Spe / 4 SpD
Jolly / Adamant nature
- Brave Bird
- Cross Poison
- Pursuit
- U-Turn
Both sets are viable. The first one, although rare, is efficace because of Crobat's access to Nasty Plot. It can be surprising and unexpected oftentimes. Air Slash and Sludge Bomb are great STAB. Heat Wave is coverage and is Crobat's only way to touch Steel-types.
The second set is much more conventional. It's the standard set. Brave Bird is very dangerous because it hits damn hard and steamrolls through mono-fighting teams. Cross Poison is STAB and hits fairies and most notably Azumarill for good damage. Pursuit hits very hard if you expect a switch. U-Turn is emergency door and hits for parting damage that's always nice.
Venomoth
Use Venomoth as a Baton Passer. It's its better set.
Obsidian (Venomoth) @ Leftovers
Ability: Tinted Lens
EVs: 184 HP / 252 Def / 4 SpA / 56 SpD / 12 Spe
Bold Nature
- Sleep Powder / Bug Buzz
- Baton Pass
- Quiver Dance
- Roost
EVs give it decent bulk while maintaining okay offensive prowess that can be dangerous after Quiver Dance. Sleep Powder puts to sleep the foe and allows some quiver dancing. Baton Pass is to be used to pass down the boost to Nidoking or Gengar (yes, I'll suggest you to use that latter). Roost keeps the moth healthy. Bug Buzz can be used over Sleep Powder if you look to avoid being Taunt-bait.
Drapion
Looks neat. I normally use Assault Vest but your variant is not bad at all.
Muk
Remember the Gengar? Well drop Muk and replace him by Gengar. That thing is a little monster! It's got great Special Attack and Speed, so it fancy Venomoth's Quiver Dance.
Use:
Gengar @ Life Orb
Ability: Levitate
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
- Shadow Ball
- Sludge Wave
- Focus Blast
- Substitute
Standard attacking set. Watch out for too many Life Orbs. You may use SubDisable if you like it better.
Gengar @ Life Orb
Ability: Levitate
EVs: 4 Def / 252 SpA / 252 Spe
Timid Nature
- Substitute
- Disable
- Shadow Ball
- Focus Blast
SubDisable is my favorite set on Gengar.
Weezing
Attacking Weezing is weak. Nidoking does that better, so opt for something else:
Weezing @ Black Sludge
Ability: Levitate
EVs: 252 HP / 252 Def / 4 SpA
Bold Nature
- Clear Smog
- Will-O-Wisp
- Pain Split
- Fire Blast
Use that to cripple foes. You may use Hex on Gengar if you plan on spamming WoW over the foe's team. Pain Split keeps that garbage as healthy as possible. Fire Blast is coverage.
