There's the obvious combo with the poison hypnotic beam coming out. But for a full blown poison deck, there are a few cards that go from medicre to playable.
-Gliscor (BC): Attack does 20 damage, auto poison, and retreat locks. I actually attempted a deck with it using Toxicroak (the poor mans terrakion). It sucked, maybe the gym card could give it the edge it needs.
-Toxicroak (BC): It becomes more than just a revenge killer. Still a poor mans terrakion, but it's at least searchable by level ball and won't get stuck active.
-The scolipede line (BC): Auto poisons when hit. This can allow scolipede to revenge kill EXs. (emerging powers whiripede is also good since you can do 70 for one if they're poisoned).
-Amoonguss (ND): Not really necessary with poison hypnotic beam doing the same thing in trainer form, but it's nice to have the option available.
-Carnivine (DE): Lure poison effectively becomes a snipe for 30, and that's not counting the additional damage they take if they don't retreat.
--Accelgor (DE): Not even Keldeo can save Terrakion from an OHKO with this.
I'm sure there's more, but those are the ones that come to mind.
-Gliscor (BC): Attack does 20 damage, auto poison, and retreat locks. I actually attempted a deck with it using Toxicroak (the poor mans terrakion). It sucked, maybe the gym card could give it the edge it needs.
-Toxicroak (BC): It becomes more than just a revenge killer. Still a poor mans terrakion, but it's at least searchable by level ball and won't get stuck active.
-The scolipede line (BC): Auto poisons when hit. This can allow scolipede to revenge kill EXs. (emerging powers whiripede is also good since you can do 70 for one if they're poisoned).
-Amoonguss (ND): Not really necessary with poison hypnotic beam doing the same thing in trainer form, but it's nice to have the option available.
-Carnivine (DE): Lure poison effectively becomes a snipe for 30, and that's not counting the additional damage they take if they don't retreat.
--Accelgor (DE): Not even Keldeo can save Terrakion from an OHKO with this.
I'm sure there's more, but those are the ones that come to mind.