Random tftsd theory (except no spoilers because I rlly want others to hear this theory-)
Ok, so. I have a theory of Mathilde being a villain, or at least not a great person, when they were alive. So far, we've found out how they were killed, we learned how the other three are tied to one another, and how Mathilde was killed ties to the others. For each of the other three characters, we've now had a negative plot point in their story, except for Mathilde. They do not remember their past, and the one person that they actually know didn't say much about them, other than how he knew Mathilde. Mathilde seemed to be very cold (up until recent episodes), as they learn more about the other characters past, we've learned very little about them, I think they're either deeply traumatized, or they deeply traumatized someone else.
Anyway, just a silly little theory