Generally any pokemon in B/W that runs Poison Heal is a nuisance. Especially in Single Battles
Pretty much the strategy will run like this.
Poison Heal Well the best thing to run here is give that pokemon a Toxic Orb.
This way once the first turn is over they'll be poisoned. Now you can't hit them any other status effect. What's worse is they'll heal every turn pratically better than that of using Leftovers. Not to mention they'll play defensively to annoy you. The only solution in mind is to kill it quickly (preferably one hit or they'll switch to something stronger to wipe out the threat and throw there wall back in).
Well there's not many choices that come to mind quickly. Especially if you're running a set team that relies on a strategy.
Here's a few ideas on beating it. However not that great.
Most ppl that run this strategy will send out there pokemon with Poison Heal first. To get there wall started up. The Toxic Orb doesn't kick in till the end of the first turn so that gives you little time to act.
Method 1: One method is to immediately hit it with a status effect that isn't poison. Paralyze will do the trick. Sleep only last a few turns. Burn can do the job too. Frozen is a bit unreliable since there's not many known ice attacks that can easily freeze a target. All in all this is rather unreliable as you're praying for the attack to work.
Method 2: as mentioned above is to kill it quickly. However the issue arises that it may take more than 1 hit to kill it. Unless you're doing Choice Band/Life Orb and STAB (Same Type attack boost) its not likely that you'll defeat it in one hit. This is cause most players will have there EVs geared towards Defense, Spec. Defense, HP, or Speed. Not to mention they'll use attacks to keep there wall safe such as Protect, Endure, Substitute (This is the worse). So usually if its in danger of dying in 1 shot they'll switch to another pokemon to take out there potential threat.
Method 3: Probably the most effective method I thought of is to use attacks that make the pokemon drop the toxic orb. Knock Off, Thief, Trick and the like can do the trick. Assumming you hit first turn. You're still dealing with Protect, etc. Trick should work. But its far better than Method 1.
Well this is all I came up with.