This one is really for a society, cause in this world that I'm building if you die then you may return as a spirit if the god of darkness or light permits you to come back, which could make killing people a really dangerous thing to do. So if there is someone that by today's standards deserves death row, for whatever the reason, how would you punish them in this world?
Well, there are a lot of variables and such that could determine something like that depending on other aspect of your setting (in-universe morals, past incidents with killing criminals, etc.). But personally I'd say basically just lock them up in a cellar and give them just enough food and water that they end up constantly on the brink of death but aren't allowed to actually die. Or possibly ship them off to some island to live the rest of their life, like how Australia was once used.
I would force them to watch various fangirls. Wait, that's not a thing? Well then. Leave them in a burning hot room. Then once they're nice and hurt but far from death, move them to a freezing cold room. Move back and forth. Oh, and did I mention you have to keep whipping them with barbed wire and rubbing salt in their wounds? If this actually kills them, mayyybe take out the rooms, and replace it with food that gives them illness - enough to make them sick until they don't want to move, but not enough to kill them.
This is going to get dark. Fates worse than death, and all that. If the technology/magic is available, these people could very well be bound and immobilized while hooked up to some kind of technological/magical life support. Like being put into a straight jacket and with a rubber funnel in their mouth while being kept fed by IV plus whatever other tortures you could imagine: temperature, sound, public shame, etc. As something perhaps more merciful, how about some way to get these spirits to die again? If spirits can interact with the living (by haunting/attacking the living), why they can't they be attacked back? If a spirit can strangle me, why can't I strangle a ghost back? Or have some good guys volunteer to be afterlife police officers when they die, to keep evildoers in check and dispatch them if necessary if they act up?
You can kill them again, but they often come back with abilities that usually make them more deadly than their living counterparts, such as teleportation and an ability that allows objects to just go right through them without them taking any type of damage.
Mhm, I guess I'd just leave them in a cube-like room providing them with food and that's about it? Maybe with like one shitty book just for funs? I mean, it's simple and to the point, and they'd end up losing their mind I suppose?
Lock them in a room and force them to watch Jake Paul, or whatever people find the cringe-worthiest nowadays. Give them a small amount of food and water. Keep them hungry or thirsty, but not starving them. Keep the room either very hot or very cold, but not to the point where they freeze or burn to death. That's probably it. I'm not a big fan of torture devices.
Torture, I would say, its excruciating and (hopefully) won't result in death. Also do you know if they are gonna come back as a spirit before they die?
I meant like is there some way of knowing if your gonna be 'brought back' as a spirit before you actually become one?
I suppose even if you do torture them, they'll die eventually and could come back as a spirit. So, perhaps there isn't a way to punish a criminal without fear of them coming back. If the law wants to punish criminals, they may have to also protect those carrying out the punishments, or try to find out how to stop a criminal from coming back (bargaining with the gods, etc).