So, I mades an AU! Its called ShatterTale, name courtesy of @elizaphant.
The basics of it is that there are three kinds of souls:
Heart Souls: These are the souls you typically see in Undertale. The monster souls have no power, but human's can have them and monsters can have the souls we typically associate with humans in Undertale.
Order Souls: These souls are similar to Heart Souls, but different. They control you. If you play MCSM, they act like the redstone chips PAMA uses.
Corrupted Souls: These souls are Heart Souls, but broken in some way. They can be taken over by an Order Soul, reviving the soul's owner and turning the soul into an Order Soul.
Chara and Asriel never went through with The Plan, but Chara has a Corrupted Soul. No other humans fell aside from Chara and Frisk.
Corrupted Soul: Chara, Grillby, Alphys, Gaster, Sans
Order Soul: Papyrus, Undyne, Nice Cream Seller (he becomes important), Asgore, Toriel
Heart Soul: Mettaton, Asriel, Frisk, Muffet
I may, or may not, write a fanfic about it.
IF I do, it will have the ships: Chariel, Asgoriel, and MAAAAYBE Muffby and Undyrus
I'll post it on my Wattpad.