Ok so I revised my team a little bit, so it's not all poison.
I haven't figured out any movesets yet, but I'm working on that part.
-Nidoking (poison-ground)
-Toxicroak (poison-fighting)
-Tentacruel (poison-water)
-Skuntank (poison-dark)
-Venusaur (poison-grass)
-Gengar (poison-ghost)
Still focusing on poison, but also being able to cover what I'm weak to.
As I mentioned before, poisoning all the opponents in the team is an unreliable strategy.
Regarding movesets:
Nidoking is well-known for being one of the best Sheer Force abusers ever made:
-Earth Power
-Sludge Bomb/Sludge Wave
-Ice Beam
-Thunderbolt/Flamethrower
Nature: Modest/Timid
EVs: 4 HP/252 SAtk/252 Spe
Item: Life Orb
Ability: Sheer Force
Toxicroak has taken a fall from grace in the new generation because of the rain nerf. It's kind of mediocre outside of rain:
-Swords Dance
-Drain Punch
-Poison Jab
-Sucker Punch
Nature: Jolly
EVs: 4 HP/252 Atk/252 Spe
Item: Life Orb/Black Sludge
Ability: Dry Skin
Tentacruel: see the Tentacruel set I posted.
Skuntank isn't that good of a Pokemon because its main role, Pursuit trapping, is better done by other Pokemon. I'd replace it with Drapion because it has the defenses to make better use of its typing. See one of my last posts for the ideal Drapion set.
Venusaur is only good in its Mega form outside of Sun teams:
-Giga Drain
-Sludge Bomb
-Earthquake/Leech Seed
-Synthesis
Nature: Relaxed/Bold
EVs: 252 HP/252 Def/4 SDef
Item: Venusaurite
or
-Giga Drain/Leech Seed
-Sludge Bomb
-Hidden Power (Fire)
-Synthesis
Nature: Modest
EVs: 252 HP/4 Def/252 SAtk
Item: Venusaurite
Gengar should use either one of these sets to take advantage of its role as a speedy special attacker:
-Shadow Ball
-Sludge Bomb/Thunderbolt
-Focus Blast
-Destiny Bond
Nature: Timid
EVs: 4 HP/252 SAtk/252 Spe
Item: Life Orb/Focus Sash
or
-Substitute
-Shadow Ball
-Focus Blast/Pain Split
-Disable/Will-o-Wisp/Focus Blast
Nature: Timid
EVs: 4 HP/252 SAtk/252 Spe
Item: Black Sludge/Life Orb