Arca Plasmor

Legendary Weapon (shotgun), requires attunement The Arca Plasmor is a Corpus-built plasma shotgun that fires highly damaging pulses of gloomium (radiation) shells. The projectiles it fires automatically debuff an enemy, have a large thickness, and innate punch through against creatures of flesh and bone, making it highly effective in mowing down large groups of enemies, but suffers from the fact it cannot score critical hits. Shotgun. The arca plasmor is a +1 magical weapon. It requires two hands to wield and has a range of 30/90 feet and depletes on a 1-2 in 20. It does 2d8 radiation damage. It cannot score critical hits. Creatures killed by this weapon are vaporised. Any equipment worn by the creature may also be vaporised (DC 10 saving throw, magic items having advantage on this roll). Pray and Spray. At the wielders discretion the arca plasmor can be used to shoot a cone attack of 30 or 90 feet. The targets must make a DEX saving throw or take full damage from the attack (or half damage on a success). Creatures at long range (31+ feet) have advantage on the saving throw. The DC of the save is based on the attack roll made by the shooter. Double Barrel. The weapon can double its damage at the cost of doubling its depletion number until the end of your next short rest. That is, it depletes on 1 to 4 in 20 but does 4d8 radiation damage. Upgradeable. The weapon can be upgraded at the Manufactorum's auto-forge to increase its plusses. To increase it you must sacrifice the gold (or equivalent robot/nannite parts) as below:

+2, 4,000 gp
+3, 9,000 gp
+4, 16,000 gp
+5, 25,000 gp
Vicious Spread. The "pray and spray" trait now has a cone of 120 feet (25,000 gp).
Hell's Chamber. The weapon now does an additional 1d8 gloomium damage (25,000 gp).
Jet Stream. This increases the speed of the shotgun's plasma arcs. Targets have disadvantage on saving throws against the "pray and spray" trait (25,000 gp).

Other upgrades maybe possible.

Gloomium
Gloomium is a poison damage type. Creatures hit by gloomium attacks have their poison resistance reduced by one step until they become vulnerable. Once vulnerable, the next time they take damage, they will also mutate on a failed DC 15 CON saving throw.

GP/XP: 9,500/1,200