The "ZW -" monsters are based off a combination of mythical beasts and weapons.
"ZEXAL Weapons" debuted during the Yuma and Astral's Duel against Kite Tenjo within the Pocket Dimension of the Emperor's Key, being created through a Shining Draw using the ZEXAL power. Each "ZW -" card is created to help Yuma and Astral overcome an opponent's monster they can't otherwise defeat. "ZW - Unicorn Spear" was the first ZEXAL weapon to be created in order to counter the banishing effect of "Galaxy-Eyes Photon Dragon" and defeat Kite. It destroyed "Galaxy-Eyes", but Kite forced a draw.
During the Battle of Sargasso, When ZEXAL was thrown into an alternate form caused by the darkness within Astral, and the subsequent initiation of ZEXAL and resulted in Dark ZEXAL, Astral performed a Dark Draw resulting in the creation of "DZW -".
Currently, the only "DZW" is "Chimera Clad", which was created to grant "Utopia Ray V" the ability to prevent itself from being destroyed in battle, as well as doubling its ATK and allowing it to attack again. It's highly unlikely anymore "DZW" will ever be created, as the conditions for Dark ZEXAL have been permanently undone.