Okay, those "prisoners of calamity" definitely used to be human, right? You don't just use terms like "prisoner" and "metamorphosis" in the context of monsters and not imply that they're cursed humans.
I don't think 獄禍 is an actual word as such (correct me if I'm wrong), but given it can apply to humans, cubes of rock and animals, I'd go for a figurative translation rather than a literal one. If you take it literally it is just "jail - evil/calamity".
We also don't know currently if they used to be humans as a rule, since one of them was, literally, a cube. We have no understanding of what they're for, how they're caused, or how they fit into anything else, in lore.
This is one of the annoying parts of translating this stuff.
獄禍 - gokuka - prison + calamity
変転 - henten - just transformation/changing forms
I'd make the argument that while "Prisoner of calamity" is sort-of accurate, but I think the meaning of gokuka is more implying that the entity/being itself is a sort-of enforced state of whatever becomes the calamity, or a container of calamity. It's more metaphorical than literal.
... However, how does one say "An entity that has been imprisoned in a mysterious malevolent calamitous form" in an elegant way without just going "prisoner of calamity", which has its own connotations.
It's 3 AM, but if I were translating this I'd probably just define a term for them and go like "Fell Vessel" for gokuka, and for gokuka henten I'd make it less clinical and say something like "The formation of a Fell Vessel".
But eh, I'm not the translator and it's been several years since I regularly spoke or wrote Japanese, so take everything I say with a grain of salt.
