Big Bertha

Cannon. Only gains an action if another creature spends an action to operate the cannon

Magic Resistance. The cannon has advantage on Saving Throws against Spells and other magical effects.

Load. To shoot the cannon must be loaded. Loading the cannon is done automatically with the Cannon Loader Mk. 4. If it is disabled, you need a DC 16 STR check to load the cannon normally.

Cannon Blast. The cannon fires one of its cannonballs. Each creature within 10 feet of the impact has to make a DC 14 Constitution Saving Throw, taking 22 (3d10 + 6) bludgeoning damage.

Lightning Blast (Recharge 5-6). The cannon shoots one of its magical lightning bullets. A bolt of lightning travels to the closest target, this target must make a DC 16 Constitution Saving Throw, taking 66 (12d10) lightning damage on a failed save, or half as much damage on a successful one. A new bolt of lightning keeps traveling to the next closest creature, until a total of 100 ft. is traveled in total.

Fire Blast (Recharge 3-4). The cannon shoots one of its magical fire bullets. A fireball is hurled at the target location. Each creature in a 20-foot-radius sphere centered on that point must make a Dexterity saving throw. A target takes 35 (10d6) fire damage on a failed save, or half as much damage on a successful one. The fire spreads around corners. It ignites flammable objects in the area that aren't being worn or carried. (lvl 5 fireball)