Corrupted magic

Your magic is corrupted by an entity which feeds on your arcane abilities.

Every time you perform magic, roll a d10 and on a roll of 1, you take 1d4 necrotic damage. For each consecutive roll which does not trigger the curse, the threshold for triggering damage increases by 1.

Each trigger of the curse manifests as a blackening of veins in a portion of the body - if the curse reduces a creature by more than half of its total hit points in 24 hours then the creature must make a constitution saving throw against their spell save DC to avoid irreversible damage to a body part as determined by the DM.