Blood Plague

You coat your blade or arrow head with a deadly concoction of tainted poisons. On a successful melee weapon attack, the target takes 2d10 necrotic damage and an additional 1d10 on their turn for 1 min. 

At the 5th level you learned how to maximize the potency of the poison increasing the duration from 1 min to 3.

At the 10th level you learned how to make the plague spread. The Blood Plague can now spread to an additional target 5ft from the afflicted target.

At the 15th level Blood Plague now does 3d10 + 10 necrotic damage.

At the 20th level Blood plague now does 4d12 + 15 necrotic damage.