The fourth season of Jackie Chan Adventures premiered on September 13, 2003 and concluded on February 14, 2004 on Kid's WB. It consisted of 13 episodes.
Daolon Wong and the Enforcers have been taken into custody and incarcerated. Planning to escape Wong attempts to summon the Shadowkhan. Instead he unleashes an ancient evil known as Tarakudo, Lord of all Oni and King of the Shadowkhan. Jackie and crew find out that the masks have been scattered across the globe and that each mask contains the power to control a different tribe of Shadowkhan as well as a different ingredient to remove and subdue the mask.
While attempting to escape from prison Daolon Wong summons Tarakudo, king of all Shadowkhan and ruler of Oni. The Chans, weary of the new evil, travel to stop him. Tohru comes face to fangs with his childhood fear. Chow comes under possession of the mask and is able to summon Shadowkhan. Learning of the legend of Tarakudo the Chans find that nine different masks exist. Nine different tribes of Shadowkhan with nine different ways to defeat them.
Traveling to Tokyo, Japan to recover the next mask the Chans are horrified when Ratso takes control of a new kind of razor Shadowkhan. Uncle and Tohru find that each mask requires a different ingredient and that Oni are repelled by onions. Tohru reads of the Hana Fuda cards, a magical deck of cards which reveals the location, mask, and removal ingredient.
Scruffy joins Jackie and Jade in the search for the Oni mask and ends up wearing it. Tarakudo controls the demon dog and succeeds in summoning bat Shadowkhan. Jade uses the powers of the ox, rat, rooster, and pig talismans to save Scruffy and winds up getting captured. Jakcie, Super Moose, Mordecai, and Eggbert team up to save Jade and Scruffy.
Intercepting the Enforcers the Chans locate the next Oni mask however in the midst of the fight Captain Black accidentally wears the mask and is able to summon a kind of sumo Shadowkhan. Hoping to persuade Black to remove the mask Jade uses the tiger talisman to split Captain Black into light and dark. Jade teams up with Light Black in order to stop Dark Black who is becoming more corrupt.
The Chans and the Enforcers fight over the next mask. Managing to snatch it away before anyone can wear it the Chans take it back to Section 13. Tohru, tired of Uncle's constant nagging, takes a vow of silence towards Uncle who also refuses to talk to Tohru. In order to learn more of the masks, Jade uses the Rat Talisman to re-animate Ikazuki, the Oni general, to learn more about Tarakudo. Sneaking out of Section 13 Ikazuki winds up attached to Finn's behind. Both Finn and Ikazuki are beyond unhappy with their current positions and Ikazuki abducts Tohru as his next host.
Paco and El Toro arrive in town to celebrate Halloween, and Paco is discouraged by the way the others treat him. He then attempts to outdo Jade in scariness by putting on the latest Oni mask. Setting out to be the scariest, he finds Tarakudo, who teaches him how to summon Shadowkhan with elastic abilities.
The Chans discover the next Oni mask in a psychic's swamp shack, but lose the Hana Fuda card that contains the Mask removal ingredient in the process and the mask ends up on Hak Foo, who summons tiny. shadow-eating Shadowkhan.
After losing a new Oni mask to an auction manager, the Chans and the Dark Hand attempt to win it in the auction. However, both teams are beaten by Valmont. He plans to use the mask to summon an army of Shadowkhan thieves, but in the ensuing fight the mask is broken in half. Valmont puts on one half, and can only summon half-Shadowkhan, Jade steals and dons the other half of the mask.
After a failed attempt at stealing a valuable statue, the Enforcers arrive at Uncle's shop seeking reform. They are granted a chance, and are employed at Uncle's shop with Tohru. When Jackie goes to transport a rare jewel to the museum, he faces three masked thugs and assumes that they are the Enforcers. When the Enforcers arrive with Jade in tow, however, they are pitted against the real thieves: Strikemaster Ice and his two cronies MC Cobra and DJ Fist.
Uncle is searching for a large source of dark Chi when the Chans encounter a mysterious girl in the junkyard. This woman reveals herself as Jade from the future, who has come back to stop the revival of Shendu by the hands of his son Drago, who has taken over in the future and now tries to secure a set of magic dragon teeth hidden in the present to ensure his father's resurrection.
Chang escapes from prison with his Chang Gang, a group of evil counterparts to the J-Team. Meanwhile, Jade wants to be recognized as a J-Team member, and places a seniority spell over the others. This backfires when, during the J-Team/Chang Gang confrontation, the J-Team members become toddlers.
The Chans arrive at an old temple in search of Daolon Wong, who has been released for good behaviour and seeks to use the magical Deja Vu stone to return to the past and reclaim his lost power. Jackie is thrown into a time vortex and travels through events of his past in hopes of finding the stone and returning home.
Jackie and Jade find the last Oni mask underwater and are surprised to find no opposition. However, when they put the mask in the vault, the masks all shatter and release the 9 Oni Generals! The demons unleash their Shadowkhan armies, who begin to cover the world in darkness. Tohru studies the legend of the Oni, and discovers a warning indicating never to bring the masks together. Now the Chans must stop all Nine Generals and their master Tarakudo.