You lash out at a creature, searing its flesh wht the spiteful fires that burn in Avernus.  Make a melee spell attack against the target.  On a hit, the target takes 10d12 fire damage, and it is branded with the mark of Zariel that is fueled by combat and suffering for 1 minute.  While branded, each time the creature takes critical damage from an attack, the critical damage is doubled.