Is this supposed to be a common? Some of the above suggestions are way too complicated for commons.
Acid Vial
Cost: 1
Effect: Deal 1 damage to target hero or ally.
Envenomed Blade
Cost: 2
Effect: When attached ally deals combat damage, the opponent is poisoned (1 dmg per turn)
Gas Mask
(item)
Cost: 1
Effect: Your hero is immune to poison damage