I've had this AU concept for a while, but I thought I'd put this here. Basically, a glitch in the timeline brings Chara back from the dead, so they fall into the underground with Frisk. All the characters are basically the same, but events are changed because there are two humans instead of one. Now, I'm not gonna make this, but if you want to, you can.
I'm not sure if someone has made this AU already, but if you wanna use this concept, credit me. logo by me