The portal cart is an interdiction rapid-response railway repair cart used in the Iron Tangle on the Fourth Floor. Its forward debris scoop generates a moving, one-way portal across the track ahead of it. An interdiction crew would normally use the cart to clear a damaged line, sending a functioning train and its passengers to a trainyard before sending wreckage into the abyss. Carl and his allies instead use the carts to evacuate stranded crawlers, hold passages against monsters, and move threats between parts of the rail system. Those uses depend on the destination setting, the cart's position, and a restrictive start mechanism that makes the vehicles difficult to operate after Station 75's transit staff have been killed.
Repair vehicle and portal mechanism
Growler Gary directs Carl to the interdiction carts at Station 75 when Carl asks how to reach friends stranded at the end of a line. Gary explains that the normal crew consists of two gnoll transit security drivers and five hobgoblin repair workers. The carts have batteries and can run when a line has lost power. He specifically recommends a lead vehicle because its front portal clears obstacles from the route. The repair yard contains several types of cart, but the portal-bearing rapid-response vehicle is distinct from the unpowered flatbeds and the smaller auxiliary carts. The latter can carry supplies and personnel without a gnoll driver; they lack the rapid-response cart's selectable debris scoop.
Ten rapid-response carts stand unused at the back of the Station 75 yard. Each has an open passenger and cargo deck, a raised enclosed driving cab, a large rear engine, and a battery compartment holding three batteries. A blade across its front becomes the lower edge of the active portal. The cart is built for the main passenger-line gauge and has its own track selector. It can draw on powered rails or use batteries, and its listed top speed is five times that of a regular passenger car. The front portal expands to fill a tunnel as the cart advances, placing anything it contacts through the chosen destination. This makes the vehicle useful for rail clearance but dangerous to anyone standing in its path.
The scoop has two destination settings: the abyss and a trainyard assigned to that particular cart. The trainyard letter is painted on the vehicle. The abyss setting releases what enters the portal over the enormous pit, while the trainyard setting can preserve passengers caught by the scoop. Selecting a different destination takes roughly ten seconds, during which the front portal goes dark. Carl later discovers that this delay matters even on a fast-moving cart: he cannot safely change its target at the last instant. The portal is one-way, and its broad reach does not make the cart itself invulnerable. A damaged track can still derail it, and an enemy approaching from the side can bypass the frontal protection.
At Station 75, the carts are launched onto chosen colored lines through separate stationary portals. Carl uses a numbered DungeonWerx selector to dial the line before a cart enters one of those gateways. The stationary route portal and the mobile scoop serve different functions: one places the vehicle on a selected line, while the other acts on whatever the vehicle encounters along that line. A cart's assigned trainyard also differs from the destination of a large portal at the end of a line. This distinction becomes decisive during the rescue, when a cart can return to one yard while the crawlers it has collected arrive at another.
Starting the Station 75 carts
The rapid-response cart's security system requires two gnoll hands on separate sensor plates in the cab. Katia tries to assume a sufficiently accurate gnoll shape, but that does not start the vehicles. Carl first attempts to use the hands of dead station staff; their remains are too badly damaged. After Mongo kills the regenerating Growler Gary, Carl tests one of Gary's hands on a plate. The other plate demands another left hand, and Carl finds that removing a hand after activation shuts the cart down. Each cart therefore needs two left hands kept in place throughout its operation.
Obtaining those hands imposes a cost on the evacuation plan. Gary initially does not understand why Carl and Donut repeatedly return to his bar with Mongo. Carl eventually explains both the mechanism and the people they are trying to save. Gary recognizes why the interdiction vehicles had remained unused after the other gnolls died and accepts the repeated deaths as a way to help avenge his friends. Carl collects fourteen left hands in all, including a spare pair for a possible seventh cart. The scene establishes that the carts' scarcity is not merely a matter of finding working machinery: their access rule survives the loss of the people meant to operate them.
Once the first cart starts, Carl dials the Sinopia Line and tests the front portal. He verifies that the abyss destination carries an environmental warning because the exit is high above solid ground; switching to the trainyard clears that warning. He then restores the intended setting. The active scoop appears as a translucent barrier across the tunnel, allowing a limited view of what lies beyond it. Carl can switch or stop it from the cab, but the hand sensors must remain engaged. The group also has to clear parked equipment from the yard before launching the larger vehicles through the route portals.
Evacuation of the abyss lines
Carl's first rescue proposal is to send a trainyard-bound cart along each of three colored lines where crawlers are trapped near the abyss. The stranded people would stand on the tracks, let the portal reach them, and arrive in a yard rather than remain at the dead end. Katia and Bautista identify two serious problems. A broken track could stop a cart before it reaches the people, and a single scoop set to a trainyard would transport wrecks, ghouls, and other monsters there before the crawlers. The party revises the plan to send two carts down each line: an abyss-bound cart to clear danger, followed fifteen minutes later by a trainyard-bound cart to collect the waiting group.
This sequence requires accurate warnings. The rapid-response carts make much less noise than ordinary trains, so someone near the end of a line might not know which cart is approaching or when to step onto the track. Carl places delayed alarm traps on all six vehicles and tests one before dispatch. Its music is loud enough to injure him slightly even at the starting point. He verifies that the first cart passes through its route portal with the scoop still active. The noise solves one problem while introducing another: the songs and their delays do not reliably tell distant crawlers which destination a particular cart is using.
The Sinopia and Grullo operations reach their waiting groups. The abyss carts go through first, followed by the trainyard carts, and roughly eight hundred people from the two groups reach positions near defended Station 36 stairwells. The carts themselves continue through the gates at the abyss end and return to trainyards rather than plunging into the pit. At Yard M, one arrives in a dead-end holding track, flips, and briefly sends part of the yard structure into the abyss before its portal shuts off. Crawlers there right it and reuse it to keep a nearby route clear. These outcomes show that dispatch is not a simple one-way trip: the carts continue moving after their intended passengers have been transported, with hazards at their return yards.
The Mindaro pair fails to produce the same result. Bautista's large group sees only one cart and remains trapped. Carl and his companions infer that the second vehicle caught the first after an obstruction slowed it; the second scoop would have sent the first vehicle to its assigned trainyard. The visible cart was therefore likely the one the group needed, but Bautista could not identify it from the alarm alone. Carl recognizes that his delayed music signals did not distinguish the carts well enough. Rather than assume the evacuees have been rescued, the party boards another rapid-response cart and drives down the Mindaro Line to investigate.
On that journey Carl keeps the scoop tuned to the abyss to clear possible monsters. After Katia sees five crawlers on the track near Station 432, he cuts the throttle and starts changing the destination to Yard E. The cart has no conventional brakes, but the ten-second change finishes before it reaches them. The five are swept into the yard instead of the abyss. Moments later, at Station 433, a crossing barrier appears over the tracks. Carl realizes too late that it is part of the station mimic. The cart's portal catches the appendage and transports the entire city boss to Yard E. The same mechanism that saves the five crawlers therefore deposits an immense predator in the place to which Carl intended to send Bautista's people.
Carl finds Bautista and about six hundred crawlers near the line's end. A view through the cart portal shows the mimic taking up a vast part of Yard E and beginning to imitate an administrative building. Carl shuts the Yard E portal and abandons that extraction route. The group instead uses the large abyss-end portal leading to Yard H, with conductor hats supplied to the evacuees. The cart still carries Carl's party through afterward. Across the three lines, Carl states that more than 1,400 people have been moved from the dead ends to places where they have a chance to survive; the portal carts accomplish much of that movement, but the final Mindaro evacuation uses the alternative portal because the cart's own destination has become unsafe.
Fixed defense at Station 36
The same forward portal can serve as a stationary barrier. During a surge of blister ghouls near the Vermillion Line, Carl parks an active cart so its scoop blocks the tunnel. Ghouls running into it vanish into the abyss. On the opposite approach, monsters that see the barrier hesitate at its edge. Carl can move the cart forward to take them one at a time or switch off the portal to fight. He recognizes that he lacks enough carts, hands, and time to protect every stairwell this way; the local defense works because the cart spans that particular passage.
Carl later retrieves two carts and brings them toward a defended Station 36. He wants to place one portal above an opening in the main chamber, but the full-size vehicle cannot pass through the narrow, turning corridors from the platform. Zhang uses the remaining charge of a shrinking wand on the cart. It becomes small enough for crawlers to push through the hall, yet keeps its weight. Once it returns to size, Carl and the others build a crane around it, using Imani's magical chains to suspend the vehicle vertically with its front facing downward. The abyss-tuned scoop opens over the chamber's central hole.
When Krakaren creatures surge through that opening, thousands fall into the suspended portal. The defenders still guard the room in case the chains, crane, or cart fail. The arrangement depends on precise placement: the scoop must face the hole, while the vehicle must stay anchored so it cannot swing away. It also reveals a limit to calling the cart merely a railway vehicle. Its portal continues to operate when the whole machine is lifted off the rails and turned into a fixed piece of defensive equipment.
Yard E and the Grull operation
Carl retains another cart for the approach to Yard E, where the displaced mimic endangers crawlers near the rail lines. It protects the party from threats directly ahead and catches a large Krakaren monster protruding over the track at Station 24, sending it through the portal. Near the trainyard, however, Carl cannot simply drive at the mimic. The giant creature can attack from outside the tunnel, and the cart must be lifted across other tracks to reach the employee line. The party withdraws into the tunnel while working out how to proceed.
In the final trainyard confrontation, the cart forms part of a timed plan involving Grull. A first summoning brings the war god into Yard E against the mimic. Zhang is to change the cart's portal from the yard to the abyss before a second summoned mantaur is sent through. That change has a ten-second interval, and the second transfer has to occur just before its summoning completes. The plan cannot treat the mobile portal as an instant escape: Carl's allies must keep the vehicle moving, select its destination, and coordinate the throw while Grull is still attacking.
Grull kills the mimic but then threatens the crawlers in the yard. Zhang drives the cart close enough for Carl and his allies to throw the second mantaur into its abyss-bound portal with about one second remaining on the summoning. Grull disappears as the transfer takes effect. The cart has thus moved both a city boss and the means of removing a god during the same crisis, although the mimic's arrival was accidental and made the rescue route unusable. Its repeated use is determined by physical positioning and timing as much as by the portal's selectable destination.