Mojo Jojo finds out that the MaleficMage girls are back and insists that they help him destroy the powerpuff girls. However they refuse and give Mojo a beating 10 times worse than the normal beating the powerpuffs do. However Mojo realizes that the reason the mages are so corrupt is because of radiation X and exposes himself to it, giving him the powers of the darkness, but as a side effect he goes insane and becomes more and more disastrous and destructive.
The powerpuff girls attack Mojo who is attacking the city, however they are easily defeated. Which is then the MaleficMage girls step in to help them and wind up defeating Mojo and reversing the radiation X's effects.
This is not the first time Mojo encountered the MaleficMage girls. The first time being when they were created and Mojo was still just a monkey lab assistant named Jojo. That time he was good friends with the MaleficMage girls since they did not make the professor's life much better than it already was.
This is the first time radiation X is shown in an episode.
The ending heart of this episode features the MaleficMage girls.