Phase 3: designing the first real round

Phase 3 is the first version of Subterrans where a match has a beginning, middle, and end.

Right now the simulation runs. Two colonies start on opposite sides of a patch, dig chambers, forage for food, grow workers, fight. One queen dies. The simulation is correct — deterministic, headlessly testable, well-specified. But a round does not have shape. There is no pressure that builds, no moment where the match turns. You play until one side wins, and the outcome feels roughly proportional to the decisions you made, but the decisions were not made in response to anything. That is a loop. It is not yet a round.

Phase 3 adds the mechanics that give it shape. Seven of them, in the order they layer in:

The spider

A neutral predator, not allied with either colony. The spider operates on a hunger clock independent of both players: it wanders, it attacks anything it finds, and when it is hungry enough it will engage ants it would otherwise avoid. It cannot be defeated by one colony alone at early-game population levels. Both colonies have to deal with it.

This introduces the first thing that happens to you that you did not cause — and that your opponent did not cause either. The early game is no longer just a race to grow. It is a race to grow while something is reducing your workers.

The threat reticle

Six to eight seconds before a spider attack lands, a reticle appears over the target area. The warning is long enough to react to — pull workers back, adjust the behavior ratio, send fighters — but short enough that the reaction has to be fast and costs something. You cannot pre-position perfectly for a threat you have not seen yet.

The reticle is a design principle as much as a mechanic. Danger that is invisible until it lands does not create decisions; it creates complaints. Telegraphed danger creates decisions. The question is whether you saw it, how fast you reacted, and whether the cost of reacting was worth paying.

The mark-priority command

A player command that designates a high-priority target — spider, enemy fighter, enemy entrance. Workers and fighters route toward it before taking other actions.

This is the player’s most direct lever over the colony’s response to a threat. Before Phase 3, the behavior ratio (forage / defend / dig) was the only coarse-grained control over what the colony was doing. Mark-priority adds a fine-grained one: not “send more fighters” in general, but “send fighters there, now.” The distinction between the two is most visible under threat, which is exactly when the difference matters.

Worker self-scatter

When danger is close, workers in the affected area move away from it without a player command. They do not fight. They do not freeze. They scatter, and return when the threat passes.

Self-scatter sounds passive, but it is the mechanic that makes the spider feel like a disruption rather than a damage event. A spider does not just remove workers — it scatters them, and scattering takes time to recover from. If workers were foraging a food pile near a spider patrol path, you lose not just the workers that got hit but the next twenty seconds of foraging efficiency while the rest return and re-establish trails. That is the middle of a round: a sequence of disruptions you manage better or worse than your opponent.

Danger pheromones

When ants encounter a threat — spider, enemy fighter, proximity to an enemy entrance — they emit danger pheromones. These propagate across the grid and decay over time, following the same two-grid pheromone system already used for food trails.

The effect: the colony remembers where things went wrong, and ants route around those areas until the pheromone fades. A spider that killed workers in a corner of the map leaves a danger signature there. Workers will forage around it. Fighters will approach more cautiously.

Danger pheromones do not require player input. They are emergent colony-level memory. But they are also visible — the pheromone overlay shows them — which means a player who reads them has information about where pressure has been and where it might return.

The reproduction lever

Food surplus above a threshold accelerates egg-laying rate and larva maturation speed. When the colony is well-fed, it grows faster. When food is contested or restricted, growth slows.

This creates a mid-game dynamic that was absent before: food is not just a resource, it is the colony’s growth rate. A player who controls more food patches earlier builds population faster, which enables defending more food patches, which compounds. The reproduction lever is the mechanism that makes early-game foraging decisions visible as late-game population differences — the thing that makes a middle exist.

It also makes the spider more interesting. A spider that disrupts foraging near a food-rich area does not just kill workers; it reduces the food flow that drives reproduction. Two disruptions, one event.

Difficulty tiers

Three settings that change how the AI opponent plays and how the world generates pressure. The differences are asymmetric: easier tiers reduce the AI’s resource efficiency and combat aggression, not just its health or numbers. Harder tiers give the AI better foraging routes, faster reaction to threat, and a world with more spider activity.

Difficulty tiers exist because Phase 3 adds enough mechanistic depth that the same settings that make the game learnable for a new player make it trivial for an experienced one. The tiers are a tuning surface. What matters for Phase 3 is that they exist and that the hardest tier is genuinely hard — that requires the spider system and the reproduction lever to be working, which is why it gets built last.

The design weekend

Phase 3 was designed over one weekend, using a three-pass Codex review process and a dual-reviewer structure: each proposal was reviewed independently by two agents before being folded into the decision journal. The seven mechanics above came out of that process.

The methodology matters only insofar as it produced a coherent phase. The seven mechanics reinforce each other — the spider creates disruption, the reticle makes disruption legible, scatter makes it expensive, danger pheromones make it persistent, the reproduction lever makes it consequential, mark-priority gives the player agency over it, and difficulty tiers calibrate how much of it there is. Designing them separately would have produced seven features. Designing them together produced a round.

What this unlocks

Once Phase 3 lands, the question shifts from “does the simulation run?” to “is the round fun?”

That is the question Phase 1 — the original PRD, written in April — said we would answer first. We are finally there. The simulation is correct. The architecture is sound. The feedback tooling is in place. Phase 3 is the first version of Subterrans that can be evaluated as a game.

What comes next

Implementation starts now, stage by stage. The spider comes first; then the reticle and scatter; then pheromones and reproduction; then mark-priority; then difficulty tiers and tuning. Each stage ships as a PR, visible in the game repo.

The devlog will be quieter while builds are happening. When Phase 3 is done, you will hear about it. In the meantime, the demo at /demo/play is the current state of the game, and the roadmap tracks where each phase sits. If you play it and something is confusing, broken, or just wrong — say so. That feedback matters more now than it will at any later point.

---

This post is a companion to A New Roadmap, which covers the updated phase structure and what changed from the old roadmap.