Arm Cannon of Dragons Breath

An arm cannon is a magic weapon that attaches to your arm, becoming inseparable from you as long as you're attuned to it. To attune to this item, you must hold it against your forearm for the entire attunement period.

As a bonus action, you can retract the arm cannon into your forearm or extend it from there. While the Cannon is extended, as an action, it can be activated to exhale its elemental energy in an adjacent 15-foot cone that you designate. Each creature in that area must make a Dexterity saving throw against a DC of 8+ Proficiency bonus + str/dex mod, taking 2d8+str/dex damage on a failed save or half as much damage on a successful one. The cannon can be used a number of times equal to your proficiency bonus per long rest. (Create a custom Action)

at level 6 the damage becomes 3d8, at level 11 it becomes 4d8 and at level 16 it becomes 5d8

Roll a d4 to determine the type of damage the cannon does when the item is identified 

on a 1 it does fire damage, on a 2 it does cold damage, on a 3 it does lightning damage, and on a 4 it does acid damage

Notes: Warforged, Damage, Combat