A demon's conscience and morals are left behind in the original body.
Obvious, because Jimmy's utterly amoral behaviour didn't start until after his first death.- Not true. Firstly, he was already at least somewhat amoral. He was planning to kill Heron Marsh in revenge for the car accident, despite the fact that the latter was seemingly brain-damaged by the accident already; and robbed a bank to further this goal. And when he tried to kill himself, it wasn't because he felt bad for what he'd done (or even for the consequences of his actions, however accidental), but because he didn't want to go to prison. Not quite psychopathic, but pretty amoral. Secondly, he doesn't lose all of his morality: His love for Sweetpea never changes, which suggests that he retains some empathy and conscience. If his morals and conscience had been left behind, it would be impossible for him to love anyone at all, even Sweetpea. Thirdly, it doesn't really make much sense for the flastical to transfer everything save for one component — especially something as complex, systemic, and emergent as morality. And lastly, his descent into near-psychopathy can be explained with regular human psychology: 1) Power corrupts. There are many things that many people don't do only because they can't get away with it. And just feeling invincible can go to someone's head; being actually invincible, forever, will go that much further. 2) Even good people will sometimes do horrible things for the sake of their freedom or the sake of someone they love. 3) Even good people can treat someone like shit if they see them as undeserving of moral consideration; it's called dehumanization, and it's one of the factors that leads to genocide. Living for so long that all things and people seem interchangeable or banal, and therefore dispensable, and therefore contemptible, effectively dehumanizes everyone and everything, thus making mass murder and mass destruction seem acceptable in the same way it made genocide seem acceptable to the Nazis or the Rwandan Génocidaires.
