Kinsey stabbed and buried her fear, only for it to reappear alive. This is because emotion can’t be killed, only buried.
All demons after taking hosts are seen eating large amounts of food and partaking in hedonistic behaviors, but eventually seem to stop or temper off, except for Eden. As shown in her memories, Eden was shamed by her mother for eating a slice of cake. Most likely, Demon!Eden is constantly eating and drinking because as a human she was constantly starving herself and not letting herself enjoy things.
Fridge Horror
It looks like ever when Dodge was vanquished with the Alpha key, Lucas stuck around, since he's an echo and can't be killed. This seems to imply that all the other people possessed by demons could be saved. Rather then using an Alpha key on them right away, the kids should have physically killed them, then summoned them to the wellhouse with the Echo key, then freed them with the Anywhere key, and only then used the Alpha key on the freed demons. By doing this procedure on all of them one by one, they could be sort of saved (though it's still not clear what exactly the echos are). If it's literally souls of the dead rendered physical and immortal, then even some living people may undergo this intentionally (minus the possession) to achieve immortality. And maybe all the dead possessed people can be resurrected as echos even now.
