A solo dev’s working-design post for Whalefall, a “traditional-ish roguelike set inside the decomposing body of a colossal deep-sea organism” — whale-shaped and mountain-sized, fallen from the sky, never seen alive. Instead of dungeon floors, a run descends through anatomical systems.

The post reads like a design essay, not a trailer: mechanics reasoning, emergent examples from the simulation, and an explicit ask about depth versus legibility.

The structure is the hook:

  • Runs travel through anatomical systems — respiratory, circulatory, digestive, neural, skeletal — with the skeletal system as a hub
  • The goal is to retrieve specimens from three systems, reach the Core, and get back out alive; specimens are roughly DCSS-rune equivalents
  • But most of the game between them is exploration and fieldwork rather than combat, spent managing light and noise while working the corpse

The core loop is investigation:

  • The corpse is full of unidentified tissues and substances, identified by observing, probing, sampling, bottling, and testing with reagents
  • Identified substances become part of a survival toolkit of flasks rather than just bestiary entries
  • Knowledge is the major form of progression — a new player sees a weird corpse; an experienced player reads its anatomy and ecology at a glance

The other big system is ecology, not monster placement:

  • Creatures react to shared world events through their own senses — sight, movement through water, blood, injury, feeding, resource availability — built as general systems rather than per-species scripting
  • Named examples: cattlefish graze and flee, lampfollowers patrol and prey, snapmouths ambush near resources, gloams filter-feed and can block line of sight, prizers bury themselves as mimics
  • The sim produces stories the author didn’t program: a fleeing creature leads scavengers toward a predator, an alerted lampfollower stumbles into a prizer and dies, blood in the water becomes another signal

Combat is deterministic and deliberately undesirable — the uncertainty comes from what fighting does to the situation around you (noise, injury, blood, scavengers, predators), not from attack rolls. Tonally it aims at the Southern Reach / Annihilation: “The corpse gets more legible. It does not get less weird.”

The most interesting tension in the post: keeping a simulation deep enough that unexpected things happen, but legible enough that players can learn it and make deliberate plans. Whalefall is early, but the systems writing is unusually concrete — worth watching how the legibility bet holds up.