Corrupting Ichor

1st-level necromancy

Casting Time: 1 action
Range: 60 feet
Components: S, M (some phlegm)
Duration: Instantaneous
Class: Druid, Sorcerer, Warlock, Wizard

You spit a globule of phlegm at one creature within range. Make a ranged spell attack against the target. On a hit, the target takes 2d8 necrotic damage. In addition, until it uses its action to wipe off the phlegm, it takes 1d4 necrotic damage at the start of each of its turns and any hit points regained are reduced by half.

At Higher Levels. When you cast this spell using a spell slot of 2nd level or higher, the damage at the start of the target’s next turn increases by 1d4 for each slot level above 1st.

Source: Heliana's Guide to Monster Hunting