Como Mojo Jojo foi criado?

Fisicamente, uma explosão de Chemical X; psicologicamente, vivendo duro e descuidado.

Da página da Wikia (grifo meu):

During the event of the creation of the Powerpuff Girls he pushed the Professor towards a container of Chemical X, which caused an explosion, mutating his simian DNA, turning his skin green and causing his intelligence and brain to enlarge, growing out of his skull. It also gave him new emotions like envy and inferiority.

[...]

After Blossom, Bubbles and Buttercup were created, the Professor lost interest and/or attention of Mojo's existence and forgot about him. With newfound intelligence, he donned a tattered overcoat with a partially shredded scarf and a paper bag to cover his brain and ran away, setting his home up in an alley. Spending time on the street by himself with no one to care about him almost immediately turned him cold and emotionless providing a motive as to why he would care to destroy Townsville and conquer the world.

Referências: o episódio Rising do Sr. Mojo e o filme O Filme das Meninas Superpoderosas .

As seen in The Powerpuff Girls Movie and the episode "Mr. Mojo's Rising", Mojo was originally Jojo, the Professor's hyperactive lab assistant who always broke everything. During the event of the creation of the Powerpuff Girls he pushed the Professor towards a container of Chemical X, which caused an explosion, mutating his simian DNA, turning his skin green and causing his intelligence and brain to enlarge, growing out of his skull. It also gave him new emotions like envy and inferiority.

Wiki das Meninas Superpoderosas

Quando as Meninas Superpoderosas foram feitas, ele empurrou o professor em direção a um Chemical X que causou a derramar na receita (dando às garotas suas superpotências) e explodiu fazendo Mojo se transformar e seu crânio e cérebro crescerem. Sua pele ficou verde. Então, as Meninas Superpoderosas nasceram e eram o mundo do Professor Utonium. Ele amava Buttercup, Blossom e Bubbles mais do que qualquer outra coisa e perdeu o interesse pelo pobre Mojo. Então, Mojo fugiu e se tornou o mal.