Flail of Tiamat

From Fizban's Treasury of Dragons, page 23.

Description
Weapon (flail), legendary (requires attunement)

This magic flail is made in the image of Tiamat, with five jagged heads shaped like the heads of five different chromatic dragons. You gain a +3 bonus to attack and damage rolls made with this flail. When you hit with an attack roll using it, the target takes an extra 5d4 damage of your choice of one of the following damage types: acid, cold, fire, lightning, or poison.

While holding the flail, you can use an action and speak a command word to cause the heads to breathe multicolored flames in a 90-foot cone. Each creature in that area must make a DC 18 Dexterity saving throw. On a failed save, it takes 14d6 damage of one of the following damage types (your choice): acid, cold, fire, lightning, or poison. On a successful save, it takes half as much damage. Once this action is used, it can't be used again until the next dawn.