A “poison” active skill attaches a “poisoned” status to an enemy. An afflicted enemy will then take damage every turn equal to the ATK of the card that used the active skill multiplied by a variable factor. The damage is dealt after normal damage calculation (i.e. after the damage calculated from combos is dealt).
For example, Lilith
poisons enemies for 1x ATK. Since Lilith has 525 ATK, an enemy poisoned by Lilith would take 525 damage every turn.
Keep in mind that inheriting a poison active on a card will use the base card’s ATK stat for calculating damage. For example, Repressive General God, Tokugawa Ieyasu
poisons enemies for 50x ATK. Since Ieyasu has 1808 ATK, an enemy poisoned by Ieyasu would take 90400 damage every turn. However, if Ieyasu was inherited on a card with a naturally high ATK stat, such as Black Dragon, Fatalis
, then the active would use the ATK stat of Fatalis (5000 after Limit Break) to calculate the poison damage; an enemy poisoned by Ieyasu’s active inherited on Fatalis would take 250000 damage every turn.