Most are designed primarily for speed, mainly due to their ability to pass between the Underworld and the mortal realm. When the vehicles reach a certain speed (indicated by a gauge on the dashboard pointing to the red zone), they can open a portal in front of themselves that leads to or from the Underworld.
A skeleton-themed cart with eerie torches on its front. Equipped to carry large loads. It must be moved by a pair of Skulkin, one pulling the cart using the bone handles on the front, and one pushing from the back.
It was only seen in "Weapons of Destiny," being pulled into Garmadon's fortress. At the gates, Kruncha stopped it so Nuckal could inspect it for any stowaway Ninja; unfortunately for the Skulkin, Nuckal's "inspection" involved throwing everything off the cart before confirming that there were no Ninja aboard.
A sleek, one-person motorcycle with a skull motif on the front. The skull doubles as the end of a built-in catapult, allowing the rider to launch unwanted guests off of the bike.
The largest of the Skulkin vehicles, a skull-faced monster truck with moving jaws and a bone hand on its rear. The latter was the vehicle's main weapon, and could be launched on a chain to grab and pull objects. It has room for multiple Skulkin, but appears to be fully functional with as few as two riders—one to drive the truck, and one to man the bone hand.
It first appeared in "Way of the Ninja," being used as the Skulkin Generals' personal transport. During the attack on the Four Weapons Blacksmith, Kruncha fired its bone hand at Nya, taking her captive. With a prisoner secured and their true objective (finding the map to the Golden Weapons) complete, Samukai returned to the truck and ordered a retreat.
The Skulkin Generals continued to use the Skull Truck during their hunt for the Golden Weapons—or rather, their pursuit of the Ninja, who constantly beat them to the legendary items. When Kai was tricked into going to the Fire Temple alone to retrieve the Sword of Fire and save his sister, the skeletons attacked the other three ninja and stole their Golden Weapons. They stored the weapons on the Skull Truck as they began heading back to the Underworld, barely achieving the necessary speed due to the Ninja's interference.
The Skull Truck was among the many vehicles stationed outside Garmadon's fortress when the Ninja dropped in. It was sucked into the Ninja's Tornado of Creation and used as part of the Ferris Wheel prison the Skulkin found themselves trapped in after the completion of the technique.
After escaping their prison, Kruncha and Nuckal somehow rebuilt the Skull Truck or retrieved a new one, which they used to reach the Mountains of Impossible Height. They snuck into the Monastery of Spinjitzu to steal the Golden Weapons for themselves, only for the plan to go completely wrong when they discovered that they could not control the power of the weapons. With that failure, the skeletons returned the weapons to their proper places and fled in the Skull Truck.
Moments before the annual Ninjaball Run began, Kruncha and Nuckal emerged from the Underworld aboard the Skull Truck, intent on participating in the race. They managed to reach the second leg of the race, Birchwood Forest, where they used the Skull Truck's bone hand to bring down Lloyd's Ultra Dragon. Unfortunately for the Skulkin Generals, the weight of the fallen dragon caused the truck to go off course, wrapping its chain around a tree before falling apart in a spectacular crash.
In a bid to destroy the Ninja by erasing them from existence, Lord Garmadon traveled back in time with the power of his Mega Weapon. He disguised himself as a Skulkin and snuck aboard the Skull Truck during the attack on Ignacia, intentionally misaiming the bone hand so it failed to capture Nya. Without their quarry, Samukai called for a retreat, and Lord Garmadon rode the truck back to the Underworld. Along the way, he overheard Nuckal commenting that he had briefly seen double at the blacksmith's shop, and realized that the Ninja of the present had followed him to the past.
When the ninja, Nya, Sensei Wu and Misako encountered Dr. Julien on the island, he revealed when Samukai revived him, he had been forced to create the vehicles and was left there.
A dragster-like Skulkin vehicle, with the front wheels replaced by treads for added traction. It accompanied the other Skulkin vehicles through the desert in "The Golden Weapon" (and the corresponding scene in "Wrong Place, Wrong Time"), and was sucked into the Tornado of Creation in "Weapons of Destiny." They made a miniature version as a polybag.