dude, i thought this should be the next episode where mojo jojo mix something in the chemical x and drop on blossom accidently and become like this... and its up too bubbles, buttercup and professor to stop her and find out how to cure her.
BUT! Not just the 3 of them, the whole townsville will help. maybe (just maybe), professor found a legend bout a samurai defeating a demon like that (you guessed it, samurai jack). so professor invent a time portal to bring find samurai jack and help them to defeat blossom, also to find a cure to this.
Actually this is from a fanfiction called "Map of the Problematique" in the Powerpuff girls section on fanfiction.net. Buttercup and Bubbles actually have to stop Blossom, and Blossom got an overdose of Aku (chemical X) after Mojo switched it with synthetic X which was killing her. Of course there's much, much more to the story than that, but it's scary how similar you got XD I'm surprised!