Murder Drones characters,(including Sam, Emily, Rebecca and Young Tessa back when she was alive.) Lackadaisy characters, Scott Takes off characters, Doki Doki Literature Club and Digimon characters.
List of Undertale aus to your story are…
Undertale Yellow, Green and Purple
Grouptale
Quatumtale
Nightswap
Glitchtale
Epictale
Crosstale
Underswap
Endertale
Magictale
Star Sanses