Curse of Balthaz is an ancient curse that was once put on the legendary Sword of Omens. It is not known who placed the curse or for what reasons. The curse would be brought on whenever the Sword of Omens was used by one ThunderCat against another. The curse is so old that only Jaga and Mumm-Ra had prior knowledge of it.
As part of his evil scheme, Mumm-Ra disguises himself as a helpless Troll called "Grygory Grygian" and tricks Lion-O into attacking Tygra with the Sword of Omens. This unleashes the curse and breaks the Sword of Omens in two, rendering it powerless.