I don't talk a lot about crossover content, but me and a friend have been brainstorming a lot of UT crossovers lately, the most recent has been the most fleshed out so far so I wanted to share.
INFINITY TRAIN AU. ( Infinity train spoilers ahead)
The traditional world of Humans in slaving monsters under a mountain has not come to pass, infact monsters don't exist in this world, not in terms of the canon storyline.
Two young boys, were on the way to a costume party, when the older one decides to take a shortcut through town to get there faster only to end up lost along the way. Frustrated and tired they begin to fight.
The younger brother having had enough runs off with the older sibling in pursuit. Trying to avoid him, the youngest opens the nearest door he can reach and jumps though not noticing the abnormally of the doorway. The eldest, terrified of loosing his brother, ignores the bright glowing vortex and jumps in after him, where they end up on the Train.
This is a time before Tulip arrived and One-One took back over as conductor.
Frustrated and confused the brothers travel from car to car meeting many if the original casts monsters along the way...but it's been almost a month and the older brother is getting desperate to get him and his sibling off this mysterious vehicle. The two have no real answers about how they got there or the strange glowing numbers on their palms. The eldest also can't figure out why his is higher then the others, but it gives him a bad feeling in his gut.
One day they are separated for a bit in one of the cars and the eldest is approached by a strange lengthy monster. He claims to be have the ability to help them get off the train. All the eldest has to do is help him with a few tasks here and there. Ignoring the warning signs, the he takes the offer and begins aiding this mysterious being.
Gaster is a monster that was created on the train, he's always been trapped in it. Sickened by his cage and fascinated by the passengers ability to disembark from it he begins to make it his life's mission to get off. Turning to science and eventually resorting to experimentation on passengers. He's made 6 attempts so far, all landing in failure, resulting in the termination of said passengers.
Asriel was one of the first, His soul becoming trapped on the train in a flower monster body, consumed with revenge and just as much of a burning desire to get off the train as Gaster.
...
After weeks of helping gaster with various scientific experiments the youngest brother gets getting suspicious of the oldest random disappearances, but wanting to keep in out of harm's way he insists that they'd get out of there soon and everything would be alright. He has no real idea the extent he's putting him and his brother in danger. In complete darkness about Gasters real intentions and previous failed experiments on passengers. All the wile his number continues to go up. He just ignores it, telling himself it's for their freedom.
Finally after almost a year if work Gasters machine to artificially give him a passengers door to our reality is finished, but in doing so he must force one if the brothers numbers to go to zero then highjack their exit door.
He convinces the oldest to finally being his brother along. Still for the most part unknowing about Gasters end game the eldest goes along with letting the lengthy skeleton strap him into the machine they've been working on.
Floweys been lurking in the shadows, monitoring Gasters progress, waiting for the perfect moment to interrupt Gasters plans. Once he sees the beginnings to the brothers exit door form he takes his chance attacking gaster. In their fight most if the machine is damaged. The eldest tries to defend Gaster, but as he's doing so Flowey reveals the monsters true plans, how he was never intending to save them and that they'd most likely be trapped in the train forever just like him.
Between the damage and the energy strain, the door and machinery implode, creating a vacuum into a between space within the tain's reality and ours. The void.
It sucks gaster in and much if the machinery before the rift closes and explodes outwards. Flowey manages to escape, but the boys are not so lucky. The eldest just manages to get his brother out before the entire car is destroyed, left in a partial rift between realities.
The shrapnel from the explosion ended up killing the two in the end, but due to the fact their numbers where artificially triggered to zero and their close proximity to the explosion their palms glow morphes into the infinity symbol while their skeletons became forever integrated into the train as monsters.
This is of course Sans and Papyrus.
Again the close proximity to the explosion left all three of them with odd abilities, including Sans's ability to teleport between cars.
For whatever reason, due it be to the explosion or transformation, only Sans and Flowey have knowledge about the fact the two used to be passengers, while poor Papyrus has no clue about ever being able to leave.
Too guilty about what he's done to them and lack of wanting to traumatized his brother, Sans does everything in his power to make sure Papyrus never finds out. In secret, much like Gaster, he tries to study about non passengers being able to leave the train.
Like the Cat he begins to collect other passengers Tapes and finds a car to stash his stuff and experiments away from Papyrus knowledge. Similar to his basement under the house in Snowden.
The boys new role on the train is to test the passangers and be gate keepers next to certain assigned car exit doors. Papyrus if course takes his job very seriously, giving the passanger vigorous puzzles to perform before being able to exit, while a passanger will probably find Sans asleep next to the exit door , only to see him at the next car door exit also. He has fun messing with them when he feels up to it.
Unable to let go of his past and the guilt, Sans keeps a small piece of his brothers tape as a necklace to remind him that he once was human and could have left the train.
