Arm cannon

An magical arm-mounted laser cannon

use an action to fire the cannon doing 2d6 radiant damage. alternatively you can use your action to charge the cannon. the cannon can hold 10 charges and deals and extra 1d6 radiant damage per charge. the cannon never runs out of ammo but requires an intelligence score of 13 to use and any shot with more then five charges knocks the user back by (5xcharges over 5)feet and if the user comes in contact with a creature or object the user and whatever they hit take half the damage of the shot. this weapon requires two hands to aim without disadvantage. if you're proficiency with this weapon you can fire it one handed without disadvantage and you can charge with a bonus action instead of an action. if you're proficient with this weapon and you're wearing heavy armor you can use a bonus action to brace before firing, negating any knockback.

It’s up to you to decide whether a character has proficiency with a firearm. Characters in most D&D worlds wouldn’t have such proficiency. During their downtime, characters can use the training rules in the Player’s Handbook to acquire proficiency, assuming that they have enough ammunition to keep the weapons working while mastering their use.

Notes: Damage, Handwear, Range, Two-Handed, Ammunition (Firearms), Reload, Slow