For everyone wondering why the S-rank monsters are able to breath in the shadow prison, they're zombies they don't need to breath.
In the last chapter (page 16) Crouch calls them Zombie Soldiers.
I love the fact that people don't get that all the monsters in his space are zombies despite seeing him both collect dead bodies and releasing them in just the previous chapter. It's hilarious
Or its somebody in a costume that uses ice magic to stay cool despite being in a glorified fursuit all day.
It's not like we saw those kinds of characters before.
@rrolo1 the monsters are undead and most likely don't need to breathe.
Its why he was stealing corpses from people ( like the one he took from the MC, which is why the MC is mad at him )