Sleven was an Anacondrai Cultist serving Master Chen. Sleven was a somewhat reluctant warrior. Although he was all for Master Chen, he was afraid of snakes and the thought of being turned into one made him nervous. Sleven's most important role was as an Anacondrai Battle Mech pilot, making him a mobile strike force for Chen's army.
After being transformed into an Anacondrai, Sleven and the Cultists began to spread out and take over Ninjago, eventually facing against the Elemental Masters and their allies at the Corridor of Elders. Chen's army proved too strong, leading Garmadon to sacrifice himself and release the original Anacondrai generals to banish Chen's followers to the Cursed Realm, including Sleven. Some time after the defeat of Chen's army, the Ninja fought against the physical manifestation of the Cursed Realm, The Preeminent. After Nya drowned the beast, the Cursed Realm was flooded and destroyed, killing the majority of its prisoners, including Sleven.
NOTE: In order to fill out the Cultist ranks, multiple copies of several Slevens appear in the series. As such, any notable appearances of an Anacondrai Cultist will be placed here, for convenience.
Sleven was briefly seen with the other Cultists at a ceremony for Chen. Once the Ninja's disguises began to rub off, Sleven was the first to notice, asking who they were. Chen demanded that the Cultists catch the Ninja, but the heroes snuck away in the confusion. However, Clouse's pet Anacondrai found them.
Sleven was one of the Anacondrai Cultists to watch the matches.
The Anacondrai Cultists watch as the Elemental Masters compete in the Thunderblade round.
Sleven tries to capture Cole as he causes mischief in the factory.
An Anacondrai Cultist was present in the noodle factory when Zugu ordered it to be locked down and after shutting off the machines, left the area. He soon returned with another Cultist to throw Dareth into the factory to work. The cultist then helped Clouse capture some of the Elemental Masters, including Shade.
Sleven watched as Chen steals the remaining Elemental Masters' powers. He attended the ceremony in which Chen steals Lloyd's power, but had to fight back the Elemental Masters when Kai and Skylor betrayed Chen.
Sleven and the other cultists were tied up at the docks, guarded by the elemental masters. When Chope and Kapau recited the spell, Sleven and his allies broke free of their bonds as they were transformed into Anacondrai. In his new state, Sleven's enhanced reflexes allowed him to counter Griffin Turner's quick blows before knocking away the Elemental Master. After the Elemental Masters retreated into the palace, Sleven and the other Cultists boarded Blade Copters to fly back to Ninjago.
After the Cultists broke into Kryptarium Prison, they fought the Ninja to obtain Pythor. With Pythor in their possession, they went back to their campsite.
Sleven and the rest of Chen's army continued their attack on Ninjago and fought against the Elemental Masters at the Corridor of Elders. When Garmadon unleashed the spirits of the original Anacondrai Generals, they banished the imposter cultists to the Cursed Realm.
Sometime after his imprisonment in the Cursed Realm, Sleven eventually transformed from his Anacondrai form back to his normal self, due to the fact that the spell to turn them into Anacondrai was never permanent.
While he is not seen nor mentioned in the episode, Sleven was imprisoned in the Cursed Realm, which is revealed to be the stomach of The Preeminent. When Morro and his army of ghosts free The Preeminent, they attack Stiix and its civilians. Eventually, the Preeminent heads out into the Endless Sea but is knocked over by a massive tidal wave created by Nya, killing the beast. As a result, the Cursed Realm is destroyed and all its inhabitants are killed, including Sleven, whose soul was promptly sent to the Departed Realm.
Sleven wears a large Anacondrai skull atop his head, with half of his face white and the other half the normal yellow. Sleven's face also has red eye-markings, furry eyebrows, and Anacondrai snake-markings on either side. His chest sports similar dual, purple markings, and he has a dark red and black belt with golden studs and Anacondrai skull-prints. The legs have two ropes; one made of silk, and another made of bones. The silk rope has two sharp teeth and two daggers attached to it. The upper half of the legs is dark red, while the lower half is purple with silver chains and claw-prints on the feet.
Sleven is a somewhat reluctant warrior. Although he is all for Master Chen, he's afraid of snakes and the thought of being turned into one makes him nervous. Sleven's most important role is as pilot of the Anacondrai Battle Mech, making him a mobile strike force for Chen's army.
- Alongside Krait, his character's model fills in the roles of generic Anacondrai Cultists in the show. Additionally, they have the same torso.
- Ironically, despite his loyalty for Master Chen and his plan, Sleven actually suffers from ophidiophobia, the phobia of snakes.
- Sleven, Ghurka, and Cole (during his days as a ghost) are the only characters to be afraid of their own kind.