For the new 2011 version, see Sword of Plun-Darr (2011 TV series).
When Ratilla tried to steal the Treasure of Thundera, Jaga stopped him using the Sword of Omens. The Sword of Plun-Darr was cast into the deepest canyon on Thundera by Jaga. Encased within the molten core of the planet, the Sword fought to free itself for years. Eventually, it caused a chain reaction which led to Thundera's destruction.
Years later when the planet began to reform, Mumm-Ra endeavored to retrieve the sword which was thought lost. The Sword was granted to him after beseeching the Ancient Spirits of Evil for it's ownership and power.
- There's a possibility that the Sword of Plun-Darr was based on the UK comic-only magical Mutant weapon called the "Scimitar of the Slain", as both are mystical Mutant weapons thought lost.