The two effects that you're looking for are Ravage Health and Creeping Ravage health.
You must have one ingredient that has both effects: Nightshade.
You must have another ingredient with Creeping Ravage Health: Fleshfly Larva
The third ingredient needs to have Ravage Health: there are multiple choices for this third ingredient. Ingredients like Emetic Russula and Stinkhorn will add a third stamina cost effect to the poison, at the cost of diluting the duration of the poison. Personally, I prefer an ingredient that just does Ravage health, so that I get the maximum duration. Nirnroot, Coprinus, Thistle, and Corn Flower can all fill that role (though Thistle and Corn Flower are in used in Weapon/Spell Power potions and are thus more valuable on the open market--Coprinus has limited uses in alchemy and is usually the cheapest option).
@FriedEggSandwich Protection Reversal poisons (that buffs you with 8% Minor Protection while debuffing your target with 8% Minor Vulnerability) make zero sense because the duration is too short compared to a straight-up Vulnerability poison (without the Protection for yourself). If you're ganking someone, you're not really concerned about what counterattacks your victim fires off within 1.6s--instead, you want to maximize damage of that initial window and kill the target before they can recover and counterattack. Keep in mind that the more effects you have, the shorter the duration (so why dilute it with Minor Defile?), and poisons made using positive effects, while granting you a buff, comes at the cost of a shorter duration. A simple single-effect Vulnerability poison (Fleshfly plus Scrib) would be far more effective (not to mention cheaper).