"Tarakudo's reign came to an end when the spirits of his generals were trapped within masks; nine generals, nine masks."
The Oni Masks are a collection of masks originating from Japan, each created by ancient Good Chi Wizards to seal the spirits of Tarakudo and his nine Oni Generals within them. The masks were then scattered to the four corners of the Earth to ensure that the Oni could never again rise to power. The hunt for them serves as the primary focus of Season 4.
Oni Masks can each summon a different tribe of Shadowkhan once the mask is attached to a host's face, but if all nine masks are brought together in one location, the masks shatter into pieces and the Oni spirits are set free, summoning enough Shadowkhan to engulf the Earth in eternal darkness.
If worn too long, the masks will possess the wearer until he/she is consumed by the demon's psyche and corrupts the wearer's chi. Depending on how much of the mask is worn by the host, the Shadowkhan will only have that much of them summoned. The wearer is also granted with superhuman strength equal to usage of the Ox Talisman, and likewise equally immense agility and reflexes. Since they are not full Oni, users are not affected by onions.
Each mask possesses the power to summon a different tribe of Shadowkhan and requires a different removal ingredient. The removal spell also requires a lizard tail, wolfsbane, sulfur root, and the left eye of a newt.
A tenth mask was forged, intended to imprison Tarakudo like the rest of his demon generals, but he got to it first and hid it in the Shadow Realm, putting it beyond the reach of any human without the use of shadow magic and the means to locate the mask.
|Mask||Oni General||Shadowkhan||Removal Ingredient||Wearer||Location|
|Rairakku||Ninja Khan||Japanese Steel||Chow||Sealed inside a chest within Shendu's Palace near Hong Kong, China|
|Murasaki||Razor Khan||Japanese Silk||Ratso||Displayed on a wall at a museum in Tokyo, Japan|
|Kiiro||Bat Khan||Japanese Rice||Scruffy||Embedded in a prehistoric exhibit at a museum in San Francisco, California|
|Midori||Sumo Khan||Rare Japanese Seaweed||Captain Black||Adorned on a totem pole situated along the Cascade Range of the Pacific Northwest|
|Ikazuki||Samurai Khan||Japanese Cherry Blossom||Finn's backside||Caught in the net of a fishing boat somewhere in the Pacific Ocean|
|Orenji||Squid Khan||Tentacle of Japanese Octopus||Paco||Embedded in the side of a towering rock formation|
|Kuro||Crab Khan||Tears of Japanese Monkey||Valmont (left half)
Jade Chan (right half)
|Held for sale at an antique dealership somewhere in the United States|
|Mosugurīn||Mini Khan||Fish||Hak Foo||Housed within a shack in the Bayou Country of the American South|
|Aka||Mantis Khan||Japanese Leaves||Nobody||Adorned on the figurehead of a sunken shipwreck beneath the ocean|
|All||All||Hair of a Samurai
(or a descendant of one)
- Most wearers will only have their faces changed to resemble those of the Oni possessing them. However, when Paco and Scruffy wore masks, their whole bodies changed to look more demonic. This could indicate that only adult humans will retain their bodily appearances (this being an exception if a child or animal dons half of a mask, such as Jade did).
- Finn was the only person who was completely conscious and didn't have his personality brainwashed while his Oni (Ikazuki) was controlling his body, due to their unusual situation (a Rat Talisman animated Ikazuki mask was accidentally fused to Finn's butt when he sat on the mask).
- With the exception of Kuro's and Mosugurīn's, the Season 4 intro segment displays each of the nine Oni Masks in the opposite order in which they were chronologically discovered. Additionally, the flashback sequence shown at the beginning of Ninja Twilight depicts Mosugurīn's Mask being removed before Kuro's. Furthermore, the Oni Masks in the vault are displayed in the following order: Rairakku, Murasaki, Kiiro, Midori, Ikazuki, Orenji, Mosugurīn, Kuro and Aka. This suggests that, despite being listed first in the official episode order, Half a Mask of Kung-Fu actually takes place after the events of The Shadow Eaters, rather than before them.