Rod of Lordly Might

The Rod of Lordly Might is a magical rod that can transform into a Mace +2, a Flaming Long Sword +1 or a Spear +3.

Baldur's Gate II: Shadows of Amn

 * City of Caverns - Reward from King Ixilthetocal if you side with him and kill Prince Villynaty, or loot from the treasury if you side with the Prince and kill the King.

In-game description
"Also called the Wrath of Three Kings, though not associated with any named king in particular, this rod was likely made in 1090 DR. It saw use during the Battle of the Bones, but for which side is uncertain, as it was found amongst the dead after a large skirmish. Three button unlock the rod's magic: The first transforms into a fearsome enchanted mace; the second, a hypnotic flaming blade, the third, a barbed spear. Only warriors can properly use its exotic mix of weaponry."