Three Oni minifigures appear in 853866, and share the same printed heads and torsos. Two of them reuse the Black Panther head topper piece, but turned around so that the "ears" become horns. All three have plain black legs, with one set being the short variety with no joints. One Oni can also be fitted with a motorcycle helmet and a recolored version of the Oni mask parts from 70643 Temple of Resurrection. The black horn elements that go with this piece were first introduced in 70795 Mask Maker vs. Skull Grinder.
The Oni originated in the First Realm, where they were bitter enemies of the Dragons. When the First Spinjitzu Master with equal measures of the Oni power of destruction and the Dragon power of creation, the two races fought to possess him. Eventually, the master fled the First Realm to escape the conflict, after failed efforts to bring peace between the two factions, and eventually brought Ninjago into being. However, the Oni were unwilling to give up on pursuing him, and managed to send a team of Oni to Ninjago to capture him. However, the Oni Mystake came to love the new world, and aided the First Spinjitzu Master in defeating her companions before settling in the realm.
Through unknown means, the three Oni Masks of Vengeance, Deception, and Hatred-each representing a different Oni warlord-made their way to Ninjago as well. When brought together to the Temple of Resurrection, they had the ability to open a portal to the Departed Realm and bring back Lord Garmadon. While in the Departed Realm, Garmadon apparently witnessed the Oni making their way to Ninjago, and thus took over Ninjago City with his Colossi and the Sons of Garmadon in an effort to prepare for their arrival. The Ninja, upon traveling to the First Realm, found the Oni absent with no trace of them but ruins, though the Iron Baron and his Dragon Hunters were seeking a means of combating them. The Oni were infamous for their shapeshifting ability, and once decimated a party of Dragon Hunters that came looking for the Dragon Armor.
Upon being defeated by Lloyd, Garmadon warned the ninja that the Oni were coming.