The Dread Seed wasn't the most powerful weapon in the galaxy but it was the most fearsome because of what it did to an ecosystem. Created by Nigrash for use in the Battle of Crystillia the Dread Seed left parts of the city uninhabitable and turned anyone in these sections into mutated zombie like monsters with growths on them and glowing eyes. However the destruction of where the device was went all the way to the core. It was a long term weapon and no counter could be made to it. Planets that had the Dread Seed would one day be uninhabitable unless secure defenses were made. Turning each planet that this was dropped one day into a "Zombie" apocalypse.