Heavily armoured. converts criticle hits to normal hits 

Heavily Weaponized. if your able to detach or render the shapeshifter cannon inoperable causing the gunner to be deprived them of their only means of attack

Cursed. when the abyssal weapon is removed the wielder will die a slowly and painfully, as their regains control and is overwhelmed with agony, as their body is replaced and penetrated with metal causing  death as the weapon is no longer sustaining their life.

Shapeshift. change in between gun types by using an action

Machine gun. 

Full auto 2d6+3 piercing damage, one target, max range of 50ft

Rapid Fire. (1 action) 3d4 piercing damage, attacks 3 targets within a 25 degree frontal arc, max range of 45ft

Fire Blast. ( 1 bonus action) 4d4 fire damage in a 25ft, cone for 3s, you can make a Dexterity saving throw of 18 subtracted by your constitution modifier to avoid the damage

Plasma Rifle. can shoot 6 times before reverting to the machine gun

Pulse Shot. 1d18 Force damage, max range of 60ft

Plasma Stream. ( 1 action) uses 3 ammo, 2d18 Force damage to any targets in a 45ft beam during 3s, you can make a dexterity saving throw of 18 to dodge the beam.

Plasma Field. (1 bonus action) Creates a field with 10ft in radius 50ft away for 6s, that does 1d10 force damage to any targets in it, halves their speed, each time the gunner shoots at the field all targets take 1d8 force damage but reduces the fields duration by a second.

Missile Launcher. when placed upwards its locks into position preventing movement and can shoot 4 times before reverting to the machine gun

Missile Salvo. single rocket which deals 1d20+5 fire damage and locks onto a spot on the ground where the player was when fired, 60ft range and the missiles have a  movement speed of 30ft

Homing missiles. (1 action) fires a single rocket which tracks the target player and when its 10ft away it splits into 3 smaller missiles, which come down and attack the 3 closest targets, dealing 1d12 fire damage in a 5ft radius. you can make a Dexterity saving throw of 18 to lose the missiles lock causing it to hit where you last were.

Mine Barrage. (1 bonus action) launch 3 mines that surge inwards towards the target before detonating in 2s dealing 3d6 fire damage in a 3ft radius.

Orbital Strike. (2 actions) fires 6 beams the move inward before a beam falls from the sky and creates a 5ft sphere dealing 1d18+2 force damage and surges outwards dealing d10+2 thunder damage 70ft away after 6s.