UnderTMNT

Imagine an AU where the core five of Teenage Mutant Ninja Turtles (Leo, Mikey, Don, Raph, and Splinter) are replaced with Undertale characters. Specifically, the various Sanses. Sans would represent Leonardo, Underfell Sans would represent Raphael, Underswap Sans would represent Michelangelo, and Beta Undertale Sans would represent Donatello. And to wrap it all up, Splinter could be represented by Gaster.