The Hidden Temple Car is actually the Infinity Train as a whole: passenger must face through multiple trials and face threats at every corner. Then they find a treasure (the problems that got them on the Train) before they race out of the temple (representing their numbers dropping and them allowed to go back home).
Moreover, there's some parallels to Mallow getting the Applewood Amulet. 1) it's wood and Mallow is a Grass-type user. 2) The team who retrieved it in the show were the Green Monkeys and Mallow has green hair and her denizen partner is Tuba the gorilla. 3) The one out of the team who got it out was the girl (with it being one of the four fabled "One-Second" Runs) like Mallow braved the Temple all by herself.
The song the troubadours play when the dragon is rampaging through the Toy Brick Car is "Crusade" by Voltaire. The song was about the narrator off to slay the dragon...and realizes to late that it's a parent with its own child. The theme of the song was about how the enemies weren't so different than the so-called Crusaders, foreshadowing the Central Theme of the car: that people despite their outward appearances aren't so different than Gladion is in some respects.
The four members of the White Gestalt actually fit the parallels of knights quite nicely with their quests and the dark sides that went into it.
Specter had a goal to help destroy an evil threat with the Ignis by following his master's orders, like a knight is in servitude to a king. He showcases a lot of apathy. only following his master's orders regardless of the damage they did.
London was on a quest to find his leader, the White Rabbit and sacrificed others for power in what he felt was an appeasement to his master and guidance.
Tokio is on his own quest to find Celebi filled with regret for not being there on a single day.
Tokio, the White Rabbit, was late for a very important date and tried using the time-traveling Pokémon Celebi to undo his mistakes.
Fitting a fanfic based on quests and fairy tales, there are a lot of parallels to The Wizard of Oz:
Dorothy must take the yellow brick road, an endless path to the Emerald City where the Wizard of Oz can help her. Gladion is on the Train and it's nothing but moving forward on an infinite journey until his quest is over and his number (which is green) goes down to zero.
London is a parallel to the Scarecrow. His realization came from him getting the brains on how his actions to appease the White Rabbit left him alone in the end. He also looks like a scarecrow what with the white suit and hat. He's also the first member to be encountered by Gladion.
Specter matches the Tin Man, a person who is in need of a heart. His body motif involves hearts, Easter is obsessed with gathering hearts and his Ignis, Earth, had a fondness for a crystal heart. He also is based on the technological based Yu-Gi-Oh! VRAINS. And his name can bring about the idiom "ghost in the machine".
Tokio is the Cowardly Lion who needs the courage in order to go back home to find his parents and make amends with Goh.
Specter's number starts growing static, reflecting how he was also a Static Character in his show.
Easter is able to get a body when they transfer themselves into Specter's Duel Disk. The symbolism comes from how they placed a hand on the deck which is what you do when you surrender a match. They give up a chance to have a human body so Specter has a chance to grow.
In Blossoming Trail, the story focuses on others knowing about the Train's existence, allowing Chloe's friends and family to learn what's happened to her. Here, only Mallow knows about the Train due to being a former passenger; everyone else presumes that Gladion has simply gone off to challenge the Island Trials. Meaning that Gladion has nobody to discuss his experiences with, and nobody other than Mallow is particularly concerned about his disapperance until Chloe learns of his adventures in Blossoming Trail.
In Voyage of Wisteria, it's revealed that what White Gestalt did was so traumatic that it had to be erased from the Train. Even Amelia forgot about them. And it's so traumatizing it makes the Cage of Flauros so tiny. So that begs the question what is Gladion going to do with the tapes that makes the Fog Car tame in comparison?
