Blood Drain

You drain the blood of a creature you can see within range.  The target must make a Constitution saving throw.  On a failure, it takes [roll]3d8[/roll] necrotic damage, gains 1 level of exhaustion, and is knocked prone.  You also gain temporary hit points equal to half the damage the creature takes.  On a success, the target takes half as much damage and isn't otherwise affected.  This spell doesn't affect creatures that don't have blood.