Vitality Syphon

You weave your magic into the blood of another creature, drawing their vitality through an unseen crimson thread. The target must make a Constitution saving throw. On a failure, the target takes 5d8 necrotic damage, and you regain hit points equal to half the necrotic damage dealt. On a success, the target takes half damage and you regain no hit points.

For the duration, you may use a bonus action on each of your turns to continue draining the creature. The target repeats the saving throw. On a failure, it takes 2d8 necrotic damage and you regain hit points equal to half the damage dealt. On a success, the spell ends.

When this spell ends, you must make a Constitution saving throw with a DC equal to 10 + the number of rounds you maintained the spell. On a failed save, you suffer one level of exhaustion.