Carl's no-win divine quest to kill the god Hellik — a death sentence whether he succeeds, fails, or walks away.
The Kill Hellik quest is the lethal bind the fire god Emberus placed on Carl: slay Emberus's brother, the god Hellik, before the end of the eleventh floor. Every path is fatal — failing or leaving the church earns a smite (usually death), and Emberus has warned that if Carl actually kills Hellik he'll kill Carl for it. That leaves only killing Emberus himself, which would mark Carl for death by all the other gods.
Both brothers are invulnerable on this floor and the next; the party has Katia's bolt to strip invulnerability for a few seconds, but even that leaves the problem near-impossible. Carl notes Hellik seemed the most sane of the gods he's met. With the eleventh floor likely truncated, the fire-fairy zealot Quemada and now Eris both press him to act, forcing the long-deferred reckoning toward the front of his mind.
A divine kill-quest with no survivable completion path, hanging over Carl across the racing floors.
Carl's unsolvable god-killing quest, the crawl's central religious death-trap.