Dark Betrayal

You can use your reaction to cast this spell whenever you cast a spell that targets a willing creature. You twist what was once a blessing into a curse, striking the target with a crippling sickness. The target must make a Constitution saving throw. On a failed save the target takes 3d8 necrotic damage and is blinded for 1 hour. On a success, the target takes half as much damage and is not blinded.   At Higher Levels When you cast this spell using a spell slot of 3rd level or higher, the damage increases by 1d8 for each slot level above 2nd. When you cast this spell using a spell slot of 5th level or higher, on a failed save the target also suffers one level of exhaustion.    

2nd Level	Necromancy
Casting Time	1 reaction, taken when you cast a spell that targets an allied creature
Range	Self
Components	Somatic	Material (a miniature dagger made from black iron)
Duration	Instantaneous
Classes	Bard	Cleric	Warlock

    Dark Betrayal