Celestial Drakefire Bombard

 Weapon, Range, very rare (requires attunement)

Firearm, 3d6! damage (40ft/120 ft), loading, two-handed , heavy

This massive, ornate cannon seems meant more for the ramparts of a castle than slung to an adventurer's back.  You gain a +2 bonus to attack and damage rolls made using the weapon. On a hit, the weapon deals an extra 2d6 radiant damage. In extremis, this weapon can also serve as a +2 maul.

When the wielder speaks a command word, the dragon legs sculpted into the cannon break free from the barrel and the talons dig into the ground.  When rooted to the ground, the cannon cannot be moved without a DC 13 strength check until the command word is spoken again.  In this configuration, the cannon fires stronger, indirect blasts.  Its range doubles, the weapon ignores terrain obstructions, the damage die doubles to 6d6!, the bonus radiant damage increases to 4d6, and all squares adjacent to the target square take 4d6 radiant damage (DC 8 + prof + dexterity for half).  The indirect nature of fire, however, means that you do not resolve the attack until the beginning of your next turn.