I was trying to sleep and my brain decided to send me a thrilling ND theory...
WHAT IF TEMPERANCE HUDSON HAD MARRIED A MARVIN. We don't know about her daughter (Charity)'s dad. That would make her not just a mentor to Bess BUT a relative of both Nancy AND Bess. Which could also explain Nancy and Bess's back and forth rivalry/frenemy situation! Hudson side vs Marvin side.
Everyone thinks Charity is the frozen hearts killer, and that is still possible. Keep in mind that if her dad was a Marvin that would make Charity BOTH which put her in the middle of the feud (if we are to say Nancy and Bess are indicative of one and their families seemed to dislike each other anyway.)
BUT WHAT IF- and hear me out...it's Charity's dad who is the frozen hearts killer? That would explain why the entity has an attachment to her doll. Maybe he went mad when she was killed (because of Temperances Hudson ties and his Marvin ties and the feud between their families. Something to do with guilt or maybe there was a curse put on any child born of both families?? Idk).
But since Temperance is a Hudson (and one of the Marvin's was a lady in white..quite possibly the one who casted her out bc of a feud!!? Maybe she lied about Tempy *gasp*) maybe Temperance was the one that put the hex on her husband, or maybe the Marvin's did or maybe something happened wbetween the families with a spell and he turned into the entity after he was driven mad and they couldn't fix it so they caged him.
Sooo maybe he freezes the hearts of men who are happy and have everything he lost. His heart "froze"/hardened when he lost his daughter and then lost the support of his wife who saw him as a liability after that??
Which would also be why he can't hurt Hudson's. If Temp has a hand in the spell that turned him into it, purposely or not, then caged him.
I wonder if Hannah is a secret Marvin as well and was sent to get rid of Temperance AGAIN for her family legacy!? And Temp is getting ahead of that by training Bess and getting her on her side, as a Marvin???
If we are to think that the Marvin's and the Hudson's powers are equal, one of them would have to get a member of the other to sway to their side to get the upper hand.
P.S- Remember Temperance told Bess she needed her to resurrect humans? Who wants to bet she needs power from both the Marvin and the Hudson side to resurrect Charity (because she was both!!!)