This device replaces the user's arm, allowing them a prosthetic limb that shoots radiant blasts. When you attune to the Arm Cannon, you are considered proficient in unarmed strikes and Radiant Blasts using it. While attuned to this item you gain +2 to spell attack rolls and your spell save DC.

Swap Modes. As a bonus action, this prosthetic arm can swap between being a cannon and an arm.

Radiant Blast. Once per turn, in place of an attack, you may make a ranged spell attack against a creature of your choice within range (120/500). On a hit, the target takes 4d6 radiant damage, and the next attack roll made against this target before the end of your next turn has advantage, thanks to the mystical dim light glittering on the target until then.

This weapon starts with 5 charges and upgrades as you level up, gaining more spells that you may cast. You regain the charges on a long rest. You may also cast the spells provided if you have a spell slot of the appropriate level to cast it with.

Level 1(5 charges): Chromatic Orb (1 charge), Detect Magic (1 charge), Gift of Alacrity (1 charge),  Witch Bolt (1 charge)

Level 5(10 charges): Enlarge/Reduce (2 charges), Fireball (3 charges), Pulse Wave (3 charges), Counterspell (3 charges), Haste (3 charges)

Level 9(20 charges): Wall of Fire (4 charges), Synaptic Static (5 charges)

Level 13(35 charges): Reverse Gravity (7 charges), Chain Lightning (6 charges), Disintegrate (6 charges)

Level 17(50 charges): Dark Star (8 charges), Time Stop (9 charges): Both of these spells can only be cast once per long rest, but still cost charges.

Notes: spellcaster