The Shadow Plague was a mysterious illness that struck the inhabitants of the island of Mata Nui prior to the coming of the Toa Mata. It was created by Makuta by reducing shadow Kraata to pure essence, then transforming that essence into an airborne virus. Those afflicted became influenced by the will of Makuta. Makuta eventually abandoned this project upon realizing that the effects did not have the same permanence that came from infected masks and that the supply of shadow Kraata was so limited as to make the effort impractical. The effects of the virus eventually faded from those afflicted, but not before large portions of the various Koro had been damaged, requiring years of repair.