Secret of the Sixth Monkey is the 6th episode of the series.
Plot
After a narrow victory against an eye creature, Antauri tells the monkeys to create new techniques by tomorrow. Chiro stumbles upon a monkey helmet and monkey glove which makes a shield. Antauri tells him of the original leader and that the glove used to belong to him. Meanwhile, in space, a strange creature finds the other glove, and brings it to the Skeleton King. He's then revealed to be the original leader, Mandarin.
After Mandarin awakens, he heads to the city and he captures Chiro and the Hyperforce. Mandarin sends the Hyperforce to the Skeleton King execpt Chiro. Mandarin wants Chiro to follow him. Chiro follows him in the beginning, but later Chiro does not accept and soon rescues the Hyperforce. They then have to fight Formless that are based of their powers, and Mandarin knows them all, except the new moves they had made up. So they defeat the Formless with the new moves. Then Manderin knocks Chiro off a building then the Hyperforce saves him and Mandarin escapes.
Trivia
After Chiro sets off the alarm and went to find the captured Hyperforce, Mandarin let off a scream which is the same sound effect used in the Ducktales episode "Earthquack," when Huey, Dewey and Louie, used a lever to stop a mine cart going over a cliff.
Allusions
Mandarin persuades Chiro to rule Shuggazoom with him, just like Darth Vader persuaded Luke Skywalker in Star Wars Episode V: The Empire Strikes Back.