Don't use this:
Venomoth @ Black Sludge
Trait: Tinted Lens
EVs: 252 Spe/252 SpA/4 HP
Timid Nature
-Quiver Dance
-Sleep Powder
-Bug Buzz
-Sludge Bomb/Hidden Power Ground
Venomoth, with Sleep Powder and QD, becomes extremely powerful after a few turns, and Tinted Lens neuters many would-be counters. Unfortunately, there are many reasons not to run this set. First of all, after a Quiver Dance Venomoth already outspaces most of the OU Metagame; being only outsped by Scarfers and Swift Swimmers/Chlorophyllers/Sand Rushers, and without a +Special Attack Nature, Venomoth doesn't hit terribly hard. It's nice to be able to use HP Ground and KO Heatran, but running that leaves it open to Skarmory, another would-be counter. Sludge Bomb gives trouble with Gengar, who is going to see a lot of usage this Generation. You might be thinking "but it's for Fairies!" Tinted Lens removes the Bug resistance that Fairies have, making Sludge Bomb trivial and niche. It does get a nice STAB boost, but it's not reliable because it only gets two attacking moves. Black Sludge is useless because Venomoth is frail and the added bulk doesn't help it at all, and it really relies on that extra power to deal damage. Plus Volcarona outclasses this set completely, so if you want to have some sort of reason to use Moth over Volc, then...
Instead use this:
Venomoth @ Life Orb
Trait: Tinted Lens
EVs: 252 Spe/252 SpA/4 HP
Modest nature
-Quiver Dance
-Sleep Powder
-Bug Buzz
-Psychic
A much better set. With Life Orb and Modest, Venomoth 3HKOs or even 2HKOs Blissey at +4 (which Venomoth isn't too unlikely to achieve) without much trouble. With Black Sludge and Timid, it barely 3HKOs. Psychic OHKOs Skarmory (and it can't really switch in on a Bug Buzz as it 2HKOs) while it 2HKOs even the most Specially Defensive of Heatran. It is 2HKOed by Fire Blast even when it's at +3 Special Defense, but it hardly matters because Venomoth outspeeds. Unfortunately this set is more difficult to use than QD Volcarona, but Sleep Powder and a smaller Stealth Rock weakness gives Venomoth its own niche over it.