At the beginning of a Poisoned enemy's turn, they take damage equal to the # of Poison stacks they have. Then the Poison stack decreases by 1.
This damage will go through an enemy's Block.
Poison can be inflicted by throwing a Poison Potion. This is one of the two ways that other classes can inflict poison. The other ways are from A Note For Yourself event when the player receives a Poison card from the Silent.