Legendary spell.
Although there were many legendary spells mastered by Wizards, Comet was always the most powerful and oppressive one!
Regardless of any enemy, Wizards with the mastery of Comet were terrifying existences.
The military fortress of the Githyankies was destroyed under the impact of Comet. The Comet smashed the steel fortress built by magic power mechanical technology of the Star Realm in a flash. The terrifying heat melted everything. The impact was just the beginning of the energy explosion, and the chain reaction behind would stay in effect for a long time. Little to no creatures could survive under the attack by Comet. Even the Avatars, who were incarnated by gods, could be killed directly. The only way to deal with Comet was to avoid it across another plane.
Under normal circumstances, any defensive spell on the same plane would break instantly!
The Githyankies lost a lot.