Arm Cannon

This weapon has a +3 to hit and +3 to damage rolls. In addition, it has the following traits

As a bonus action, you can cycle this weapon's damage types between Cold, Force, Lightning, And Fire

A number of times equal to your proficiency bonus you can make an unique attack that differs between what damage type the weapon is using

Force: Super missile. Deals 4d10 force damage in a 15 foot radius.

Cold: Ice spreader. Deals 8d10 Cold damage to a single target. Can freeze the target for 1 round on a d20 roll of 15 or higher

Lightning: Wavebuster. Deals 2d10 lightning damage. Can be sustained for 4 rounds without rerolling to hit

Fire: Flame thrower. Deals 3d10 fire damage to all creatures within a 15 foot long 10 foot wide line. can be sustained for 3 rounds without rerolling to hit

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: Bonus: Magic, Living creature, Damage, Combat, Range, Ammunition (Firearms), Reload, Vex