A plot spell you'll only consider when even killing something won't make it die. Inversely, it's a threat even to PCs at high levels, since now nothing can raise them, which is one of the fates worse than death (if only because death is cheapened) from a deck of many things.
Note that you really want the thing that can't die to be at least unconscious, though, because this spell manages to cram in every possible way a spell can fail. You need to (A) touch attack the creature, (B) beat their SR, (C) have them fail the save. Anything that's worth casting this spell on will likely make all of those difficult. Oh, but if you didn't sleep through the loredump, at least the monster gets a -4 on its will save, which at this level could be in the 30s. Again, try to go for some nonlethal damage and knock it out so you don't have to deal with the touch and save.
There is still a way to get the target out, and anyone who can cast [the SL 9 spell to free them](https://aonprd.com/SpellDisplay.aspx?ItemName=Freedom) can cast the Wish (or Miracle if they have a cleric buddy) it takes to find them. Therefore, if you seal the Dark Lord away so his minions cannot raise him, you're going to have to make up some holy order and get them to build a castle with a *really nice treasury* only accessible to someone of their bloodline or whatever directly on top of wherever you cast this spell, because the climax of the first act of the next campaign is going to be someone breaking the seal on the Dark Lord.
How far into the ground someone gets put isn't really specified, so it's hypothetically possible to just *mine* a chunk of ground out and take the prison with you, possibly in a bag of holding, which would at least be safer than leaving them in whatever random diabolic lair you encountered the boss in.
Basically Plot/NPC spell, IMO. Unless there's some super specific enemy that needs to be imprisoned vs killed (which I would consider plot reason), I doubt a PC would use this.
Dying isn't the worst thing that can happen to your character, getting permanently stuck is. This is one of the ways of getting permanently suck, plan accordingly.
A plot spell you'll only consider when even killing something won't make it die. Inversely, it's a threat even to PCs at high levels, since now nothing can raise them, which is one of the fates worse than death (if only because death is cheapened) from a deck of many things. Note that you really want the thing that can't die to be at least unconscious, though, because this spell manages to cram in every possible way a spell can fail. You need to (A) touch attack the creature, (B) beat their SR, (C) have them fail the save. Anything that's worth casting this spell on will likely make all of those difficult. Oh, but if you didn't sleep through the loredump, at least the monster gets a -4 on its will save, which at this level could be in the 30s. Again, try to go for some nonlethal damage and knock it out so you don't have to deal with the touch and save. There is still a way to get the target out, and anyone who can cast [the SL 9 spell to free them](https://aonprd.com/SpellDisplay.aspx?ItemName=Freedom) can cast the Wish (or Miracle if they have a cleric buddy) it takes to find them. Therefore, if you seal the Dark Lord away so his minions cannot raise him, you're going to have to make up some holy order and get them to build a castle with a *really nice treasury* only accessible to someone of their bloodline or whatever directly on top of wherever you cast this spell, because the climax of the first act of the next campaign is going to be someone breaking the seal on the Dark Lord. How far into the ground someone gets put isn't really specified, so it's hypothetically possible to just *mine* a chunk of ground out and take the prison with you, possibly in a bag of holding, which would at least be safer than leaving them in whatever random diabolic lair you encountered the boss in.
Honestly pointless if you ask me, Trap The Soul is a much better way to permanently imprison something that won't stay dead.
Basically Plot/NPC spell, IMO. Unless there's some super specific enemy that needs to be imprisoned vs killed (which I would consider plot reason), I doubt a PC would use this.
Dying isn't the worst thing that can happen to your character, getting permanently stuck is. This is one of the ways of getting permanently suck, plan accordingly.