|“What is that? A truck?”|
“That is no truck. It is a moving fortress.”
|— Kai and Wu, "The Rise of the Great Devourer"|
The Serpentine Train was a Serpentine vehicle. It used a "Tour Ninjago" bus, but was infected by the Fangpyre's bite, effectively transforming it into a heavily armed (and heavily armored) mobile fortress for the Serpentine's use. The Serpentine used this to go to Ouroboros.
While Pythor retrieved the Fangblades from the Ninja, Skales ambushed a Tour Ninjago bus with a group of Serpentine, commandeering it for their use. When Pythor arrived, he boarded the bus with his minions and ordered the Tour Bus Driver to drive them to the Lost City of Ouroboros. When Skales noticed the Ninja in hot pursuit, Pythor had a group of Fangpyre Scouts and Soldiers bite the bus to transform it into the Serpentine Train.
As the Ninja gained on the new Serpentine vehicle, the train attacked Cole with its tail as Fang-Suei and Chokun emerged from the sides of the rear car inside small turrets. Between the tail's attacks, a barrage of lasers from the turrets, and a pack of Bite Cycles launched from the middle of the train, the Ninja were kept at bay until Zane came up with a plan; while Nya and Jay drew the turrets' fire, the White Ninja managed to jump on top of the train and detach the rear car by freezing and shattering its coupling with the Shurikens of Ice.
Noticing the Ninja boarding the train, Pythor demanded that the vehicle goes at full speed. The Tour Bus Driver protested that going any faster would risk blowing up the engine, but Pythor simply threw him off the train before pushing the engine to its limit, setting the front of the train alight. Meanwhile, the Ninja decided to race each other to the front car, infiltrating the train separately to fight off the Serpentine. After defeating most of the snakes (including Skales) and reuniting between the front two cars, the Ninja spotted Pythor in the front with the Fangblades.
Before they could burst into the car, Master Wu dashed across the final coupling before detaching the rest of the train. Believing that the Ninja had a greater destiny ahead of them, Master Wu confronted Pythor alone, and the two battled until the train's overworked engine finally gave out, causing the entire front car to crash right outside Ouroboros. Neither Pythor nor Master Wu was harmed in the crash, but the Anacondrai General recovered first, taking the Fangblades into the city to revive the Great Devourer—once Master Wu climbed out of the rubble, he quickly pursued the Snake King.
Meanwhile, the Ninja were left in the inactive remnants of the Serpentine Train, complaining about Master Wu leaving them behind. Fortunately, Lloyd flew in on the Destiny's Bounty, using the ship's anchor to hook the train and carry it to Ouroboros. It is unknown what happened to the Serpentine Train afterward, but it was likely consumed by the Devourer or left to sink into the Sea of Sand.
- The Serpentine Train was built as a possible Ninjago set but didn't make it past the prototype stage. Consequently, the television series is its only "official" appearance.
- The Serpentine Train displays notable differences from the prototype set. In addition to larger cars (a common change from playset to TV vehicle) and a ridge of green spines along its "back", the front car of the TV version has slightly less snake-like features than the playset would have had (including a visor-like windshield instead of the separate eyes of the prototype). Overall, the TV version of the train looks more like a bus or a truck, while the set resembled a standard train with a locomotive engine.