Okay so how many aus do we have branching off from that base thread?
Obviously there's the one they all came from, which is just a normal doctor who/undertale crossover, separate universes, the doctor managed to get gaster out of the void and they built a portal to visit each other and explore other universes (hopefully they'll be able to explore the hollow knight one soon hehehehehe). Pre-events of undertale, the doctor adopts flowey/asriel and chara, finds jenny, marries jack, and gaster visits so often that he's pretty much a part of the family too.
Then there's the one extremely similar to that one but chekilli also died during the war and they're slightly behind the main one so the versions of gaster and the doctor in the main one can warn the versions of themselves in this alternate one about possible things beforehand, and they've started to become less similar because of this.
Then there's the one I've just been talking about, the companion one, where what if the universes were one and the same so timelords have magic and the doctor rescues wingdings from the war before he's thrown into the barrier. Normally I headcanon gaster as aroace but he's not in this one and gets a crush on an alien girl that they meet in their travels. Arrow comes from elsewhere.
Then, branching off of that, if timelords have magic then what if they also have monsters, and if so what if wingdings was a gallifreyan monster? Turns out most timelords are not good at taking care of monsters cuz they believe them to just be spells and tools, but the doctor sees them as the people they are and becomes close friends with wingdings from an early age.
Then, branching off of that, another one where what if wingdings wasn't aroace, but this time he falls for the doctor and also the master isn't a horrible jerk and goes by the rebel instead. Got another fanchild oc here named Circ, short for Circular Gallifreyan.
And then we've got like nine smaller side aus.