Boil Blood

Choose a target whose drop of blood you can acquire, such as from having it on you or moving and spending a bonus action to touch the skin where the bleeding resides. You cause the target's blood on the inside to boil, infecting it with your magics. The creature takes 2d6 acid damage when you cast the spell and has disadvantage on attack rolls and ability checks as their body's temperature rises, begin to sweat, and writhe in internal pain. Until the spell ends you can use a bonus action on each of your subsequent turns to cause this damage again. 

This spell has no effect on creatures without blood in their bodies.

At Higher Levels. When you cast this spell using a spell slot of 3rd level or higher, the damage increases by 1d6 for each slot level above 2nd.