Infernal Cannon

This blackened metal cannon is embedded with infernal runes that pulsate ominously. Once per day, you can use an action to blast a 30-foot line that is 5 feet wide. Each creature in that line must make a Dexterity saving throw, taking 6d10 fire damage on a failed save, or half as much damage on a successful one. If this cannon is used while you are attuned to it, you gain resistance to fire damage for 24 hours. Additionally, you can once per long rest reroll a failed attack roll made with the cannon, but you must take the new result even if it is lower.