Alrite, here we go!
What is Altertale?
Altertale is an Undertale AU, a universe where Sans has switched roles with Toriel, Papyrus with Asgore, and Gaster with Asriel. There are no other swapped characters in this AU, meaning only Sans, Papyrus, Toriel, Asgore, Asriel, and Gaster have been altered in this AU. Everything else remains mostly unchanged.