Agonizing Mark

You choose a creature you can see within range to mark as your prey, and a ray of black energy issues forth from you. Until the spell ends, the first time each turn you deal damage with an attack the target must make a Constitution saving throw. On a failed save, it falls prone as its body is filled with torturous agony. 

At Higher Levels: When you cast this spell using a spell slot of 2nd level or higher, you may target one additional creature per spell level above 1st.