When you hit a creature with Tyrfang, you can expend one spell slot to deal fire damage to the target, in addition to the weapon’s damage. The extra damage is 2d8 for a 1st-level spell slot, plus 1d8 for each spell level higher than 1st, to a maximum of 5d8. The damage increases by 1d8 if the target is a lycanthrope or changeling, to a maximum of 6d8.