I was curious about the Heat Metal spell. I have a Cleric in my party that has been using it to add to his damage by casting it on his weapon. Does the attack he makes deal added damage instantly or does he use a bonus action to add it? Or does it work that way? If you cast heat metal on a weapon you're holding, you take the damage.
— Jeremy Crawford (@JeremyECrawford) 7 maggio 2018