Clockwork Mace of Divinity 2014
Weapon, uncommon, (requires attunement)
This clockwork mace is composed of several different metals. While attuned to this magic weapon, you have proficiency with it. As a bonus action, you can command the mace to transform into a trident. When you hit with an attack using this weapon's trident form, the target takes an extra 1d6 radiant damage.
Source: Vault of Magic (Kobold Press) · License: OPEN GAME LICENSE Version 1.0a details