Monotype Team

Poison types. Yeah. Help?

Drapion (M) @ Leftovers
Trait: Battle Armor
EVs: 252 HP / 4 Def / 252 SDef
Careful Nature (+SDef, -SAtk)
- Toxic Spikes
- Whirlwind
- Crunch
- Earthquake

Toxicroak (M) @ Expert Belt
Trait: Poison Touch
EVs: 4 HP / 252 Atk / 252 Spd
Adamant Nature (+Atk, -SAtk)
- Swords Dance
- Stone Edge
- Brick Break
- Sucker Punch

Crobat (M) @ Black Sludge
Trait: Inner Focus
EVs: 252 HP / 4 Def / 252 Spd
Jolly Nature (+Spd, -SAtk)
- Brave Bird
- Taunt
- Roost
- Super Fang

Nidoking (M) @ Life Orb
Trait: Sheer Force
EVs: 4 HP / 252 SAtk / 252 Spd
Modest Nature (+SAtk, -Atk)
- Earth Power
- Ice Beam
- Thunderbolt
- Fire Blast

Gengar (M) @ Choice Specs
Trait: Levitate
EVs: 4 Def / 252 SAtk / 252 Spd
Timid Nature (+Spd, -Atk)
- Shadow Ball
- Thunderbolt
- Focus Blast
- Hidden Power [Ice]

Scolipede (M) @ Focus Sash
Trait: Swarm
EVs: 4 HP / 252 Atk / 252 Spd
Jolly Nature (+Spd, -SAtk)
- Protect
- Megahorn
- Rock Slide
- Earthquake

Drapion: Use Battle Armor as the ability (you're not attacking with it and Battle Armor is best suited for defensive/supporting sets). Have it hold Leftovers of Black Sludge

Poison Touch is gimmicky with Toxicroak. To help against rain teams, use Dry Skin instead. You can also use Ice Punch instead of Stone Edge for Gliscor and Landorus.

Crobat is more of a stall breaker, so Flying Gem has no use on it unless you're using Acrobatics:
-Brave Bird
-Taunt
-Roost
-Super Fang/Toxic/U-turn
Nature: Jolly
EVs: 252 HP/4 Def/252 Spe
Item: Black Sludge/Leftovers

Gengar is too fast for Choice Scarf. How about you try this out, instead?:
-Substitute
-Disable/Pain Split
-Shadow Ball
-Focus Blast
Nature: Timid
EVs: 4 HP/252 SAtk/252 Spe
Item: Leftovers/Life Orb

TBH, Venusaur and Victreebel are useless unless they're in sunlight, which can be set up by Ninetales. In one slot, you can use Roserade to set up Spikes:

Spiker:
-Spikes
-Giga Drain/Grass Knot
-Hidden Power (Fire/Ice)
-Stun Spore/Leech Seed/Rest
Nature: Calm
EVs: 252 HP/120 Def/136 SDef
Item: Leftovers
Ability: Natural Cure

You can also have Nidoking as an all out attacker:
-Earth Power
-Ice Beam
-Thunderbolt
-Flamethrower/Fire Blast/Sludge Wave
Nature: Modest/Timid
EVs: 4 HP/252 SAtk/252 Spe
Item: Life Orb/Choice Specs/Choice Scarf
Ability: Sheer Force

Will test those out. Thanks for the input!

Updated team. Check the OP

Scolipede is too weak offensively, unless it runs Swords Dance instead of Protect. That, or it can serve as a Spiker:
-Swords Dance
-Megahorn
-Earthquake
-Rock Slide
Nature: Jolly
EVs: 252 Atk/4 Def/252 Spe
Item: Life Orb
Ability: Swarm

Or you can use it as a Spiker:
-Spikes
-Toxic Spikes (this is only if Drapion can't get them up on time)
-Megahorn
-Earthquake/Rock Slide
Nature: Jolly
EVs: 4 HP/252 Atk/252 Spe
Item: Focus Sash
Ability: Swarm

As I said before, use SubSplit or SubDisable Gengar. They're more effective than Choice Specs and Gengar can afford 2 moveslots for offensive moves (since Shadow Ball and Focus Blast have perfect coverage). SubSplit Gengar allows it to beat Blissey 1 on 1, while SubDisable can mess up opponents that have only 1 move that can hit Gengar (like Conkeldurr).

Also, like I mentioned use Dry Skin on Toxicroak. I forgot to mention this, but Poison Touch doesn't serve much use when 2 layers of Toxic Spikes are up.

I personally don't think you should pick Scolipede or Toxicroak. Toxicroak can be good when used with a rainy strategy but unless you know you can set him up with that then I wouldn't go for it. Giving him Rain Dance isn't any good either because he's not really likely to survive long enough. Scolipede, in my opinion, is generally bad.

If I was putting together a Poison team, I'd go for Gengar, Drapion, Venusaur, Venomoth, Crobat and Tentacruel, but that's just me. Tentacruel does well as a Special defensive with Barrier, provided you can ensure he doesn't get hit by too many physical moves. Venusaur, obviously, is generally good. Venomoth can run Quiver Dance, which again has a risk of physical weakness, but I think it's worth it as long as you can back some of your other more Defensive Pokémon up with some extra Def EVs or Defense increasing for the situation. Crobat isn't as good as it seems, but I do think he has potential with Acrobatics and Flight Gem, along with some other stuff you could throw in there.

My only gripe with Poison oriented teams is that they all share a similar weakness...Your objective is to find a way to negate it completely or at least try to weaken it's effect on you.

Steel types will completely nail with as they are immune to Poison attacks/status effects. So you could go for Pokemon who can use Fire/fighting/ground type moves. (Good move on Toxicroak.)

Another thing you should worry about....Psychic and ground types...Most Psychic types like Alakazam (specifically with Magic Guard) are pretty much acting steel type because of the ability Magic Guard. They will also be generally faster them most poison types save for Gengar. Certain ground types will decimate your ability to poison them on the spot (I.E Excadrill, The Nido family). Some will be fast enough to land a hit before they do (Krookodile is amazinlgly fast).

Consider all the elements you will go up against when you want to fight using poison type Pokemon.

Another type that ever monotype will and must face that I think you'll have a hard time taking out....Dragons...Dragons are tough enough to laugh off you'r poison effect and they are pretty much immune to it thanks to the move safeguard. So pack some dragon and or ice moves to take care of it.

Thanks all I have to say in the matter! Best of luck!

First of all, for your leads, I would either choose crobat or gengar over drapion.

Crobat's immunity from flinches makes it an expert for dealing against fake out leads, most notably infernape and meinshao, and with 130 base speed it will have no trouble outspeeding either of them and 2hitkoing (1hitKO if they aren't holding focus sash).

Aside from that, I think you need some more ground-resistance. I'd fit Weezing in your team (maybe in place of toxicroak or scolipede). It has access to flamethrower, dealing with any steel that might get in your way, send out will-o-wisp to cripple your opponents and haze to erase stat boosts.

@Webdemon: I've encountered an absolute pro who uses a mono-poison team. They are actually quite difficult to deal with once used correctly. Pyschic teams are a definitive threat, however. Alakazam is faster than Gengar by 10 points, so that is not a counter, this guy made a good move in including Drapion on the team, however.