Arcane Cannon

From Explorer's Guide to Wildemount, pages 265-266.

Description
Wondrous item, very rare.

This Large cannon is imbued with magic. It requires no ammunition and doesn't need to be loaded. It takes one action to aim the cannon and one action to fire it. After the cannon has fired, it must recharge for 5 minutes before it can be fired again.

The creature firing the canon chooses the effect from the following options:

Acid Jet. The cannon discharges acid in a line 300 feet long and 5 feet wide. Each creature in the area must make a DC 15 Dexterity saving throw, taking 22 (4d10) acid damage on a failed save, or half as much damage on a successful one. In addition, a creature that fails its saving throw takes 11 (2d10) acid damage at the start of each of its turns; a creature can end this damage by using an action to wash off the acid with a pint or more of water.

Fire Jet. The cannon discharges fire in a line 300 feet long and 5 feet wide. Each creature in the area must make a DC 15 Dexterity saving throw, taking 33 (6d10) fire damage on a failed save, or half as much damage on a successful one. The fire ignites flammable objects the area that aren't being worn or carried.

Frost Shot. The cannon shoots a ball of frost to a point you can see within 1,200 feet of you. The ball then expands to form a 30-foot-radius sphere centered on that point. Each creature in that area must make a DC 15 Constitution saving throw. On a failed save, a creature takes 22 (4d10) cold damage, and its speed is reduced by 10 feet for one minute. On a successful save, a creature takes half as much damage, and its speed isn't reduced. A creature whose speed is reduced by this effect can repeat the save at the end of each of its turns, ending the effect on itself on a success.

Lightning Shot. The cannon shoots a ball of lightning to a point you can see within 1,200 feet of you. The lightning then expands to form a 20-foot-radius sphere centered on that point. Each creature in that area must make a DC 15 Dexterity saving throw. On a failed save, a creature takes 33 (6d10) lightning damage, or half as much on a successful one. Creatures wearing metal armor have disadvantage on the save.

Poison Spray. The cannon expels poison gas in a 60-foot cone. Each creature in that area must make a DC 15 Constitution saving throw. On a failed save, the creature takes 22 (4d10) poison damage, and is poisoned for 1 minute. On a successful save, the creature takes half as much damage and isn't poisoned. A creature poisoned in this way can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.