diff --git a/core/src/Spawning.cpp b/core/src/Spawning.cpp
index 2e7c7d1..6fce226 100644
--- a/core/src/Spawning.cpp
+++ b/core/src/Spawning.cpp
@@ -312,3 +312,187 @@ SpawnerTickResult tickSpawnerBlock(SpawnerBlockState& spawner, const SpawnEnviro
     SpawnerTickResult outcome;
     outcome.delayAfter = spawner.delay;
 
+    Vec3 blockCenter = behaviorCellCenter(spawner.position);
+    outcome.playerInRange =
+        env.playerPresent && straightDistance(blockCenter, env.playerPosition) <=
+                                 spawner.activationRange;
+    if (!outcome.playerInRange) {
+        outcome.denial = SpawnDenial::TooFarFromPlayer;
+        return outcome;
+    }
+
+    if (spawner.delay > 0) {
+        --spawner.delay;
+        outcome.delayAfter = spawner.delay;
+        return outcome;
+    }
+
+    if (nearbyOfKind >= spawner.nearbyLimit) {
+        outcome.denial = SpawnDenial::CategoryCapReached;
+        spawner.delay = behaviorRandomRange(spawner.rng, spawner.minDelay, spawner.maxDelay);
+        outcome.delayAfter = spawner.delay;
+        return outcome;
+    }
+
+    for (int index = 0; index < spawner.spawnCount; ++index) {
+        int dx = behaviorRandomRange(spawner.rng, -spawner.spawnRange, spawner.spawnRange);
+        int dy = behaviorRandomRange(spawner.rng, -1, 1);
+        int dz = behaviorRandomRange(spawner.rng, -spawner.spawnRange, spawner.spawnRange);
+        Vec3i probe{spawner.position.x + dx, spawner.position.y + dy, spawner.position.z + dz};
+        if (!env.world->solidAt(probe.x, probe.y - 1, probe.z)) continue;
+        if (!hasSpawnRoom(*env.world, probe, spawner.requiredHeadroom)) continue;
+        outcome.positions.push_back(behaviorCellCenter(probe));
+    }
+
+    if (outcome.positions.empty()) {
+        outcome.denial = SpawnDenial::NoHeadroom;
+    } else {
+        outcome.fired = true;
+        spawner.totalSpawned += static_cast<int>(outcome.positions.size());
+        ++spawner.cyclesFired;
+    }
+
+    spawner.delay = behaviorRandomRange(spawner.rng, spawner.minDelay, spawner.maxDelay);
+    outcome.delayAfter = spawner.delay;
+    return outcome;
+}
+
+Spawner::Spawner() : ruleTable(defaultSpawnRules()) {}
+
+Spawner::Spawner(std::vector<SpawnRule> rules, const MobCap& caps)
+    : ruleTable(std::move(rules)), capTable(caps) {}
+
+const SpawnRule* Spawner::pickRule(const SpawnEnvironment& env, SpawnCategory category,
+                                   uint64_t seed) const {
+    int totalWeight = 0;
+    for (const SpawnRule& rule : ruleTable) {
+        if (rule.category != category) continue;
+        if (rule.dimension != env.dimension) continue;
+        if (rule.weight <= 0) continue;
+        totalWeight += rule.weight;
+    }
+    if (totalWeight == 0) return nullptr;
+
+    int pick = static_cast<int>(seed % static_cast<uint64_t>(totalWeight));
+    for (const SpawnRule& rule : ruleTable) {
+        if (rule.category != category) continue;
+        if (rule.dimension != env.dimension) continue;
+        if (rule.weight <= 0) continue;
+        pick -= rule.weight;
+        if (pick < 0) return &rule;
+    }
+    return nullptr;
+}
+
+SpawnTrial Spawner::planSpawn(const SpawnEnvironment& env, SpawnCategory category,
+                              const Vec3i& chunkColumn, uint64_t seed, int attemptIndex) const {
+    SpawnTrial trial;
+    trial.category = category;
+
+    uint64_t ruleSeed = spawnHash(seed, chunkColumn.x, attemptIndex, chunkColumn.z, 0x11);
+    const SpawnRule* rule = pickRule(env, category, ruleSeed);
+    if (rule == nullptr) return trial;
+
+    trial.ruleFound = true;
+    trial.species = rule->species;
+    trial.category = rule->category;
+
+    if (!pickSpawnCell(env, chunkColumn, seed, attemptIndex, trial.cell)) return trial;
+    trial.cellFound = true;
+
+    uint32_t packRng =
+        static_cast<uint32_t>(spawnHash(seed, trial.cell.x, trial.cell.y, trial.cell.z, 0x9c));
+    trial.packSize = behaviorRandomRange(packRng, rule->packMin, rule->packMax);
+    return trial;
+}
+
+SpawnResult Spawner::attemptSpawn(const SpawnEnvironment& env, const SpawnRule& rule,
+                                  const SpawnTrial& trial, uint64_t seed) {
+    SpawnResult result;
+    result.species = rule.species;
+    result.category = rule.category;
+    result.role = roleForSpecies(rule.species);
+    result.origin = trial.cell;
+    result.denial = checkSpawnRule(rule, env, trial.cell, capTable);
+
+    if (result.denial != SpawnDenial::None) {
+        ++denials[static_cast<std::size_t>(result.denial)];
+        return result;
+    }
+
+    uint32_t rng = static_cast<uint32_t>(
+        spawnHash(seed, trial.cell.x, trial.cell.y, trial.cell.z, 0x9c));
+    result.positions = spreadPack(rule, env, trial.cell, trial.packSize, rng);
+    result.spawned = true;
+    ++spawned;
+    return result;
+}
+
+SpawnResult Spawner::runColumn(SpawnEnvironment& env, SpawnCategory category,
+                               const Vec3i& chunkColumn, uint64_t seed, int attemptIndex) {
+    SpawnTrial trial = planSpawn(env, category, chunkColumn, seed, attemptIndex);
+
+    SpawnResult result;
+    result.category = category;
+    result.species = trial.species;
+
+    if (!trial.ruleFound) {
+        result.denial = SpawnDenial::NoRuleMatched;
+        ++denials[static_cast<std::size_t>(result.denial)];
+        return result;
+    }
+    if (!trial.cellFound) {
+        result.denial = SpawnDenial::NoStandableCell;
+        ++denials[static_cast<std::size_t>(result.denial)];
+        return result;
+    }
+
+    uint64_t ruleSeed = spawnHash(seed, chunkColumn.x, attemptIndex, chunkColumn.z, 0x11);
+    result = attemptSpawn(env, *findSpawnRule(ruleTable, trial.species), trial, ruleSeed);
+    if (result.spawned) env.addPopulation(category, result.packSize());
+    return result;
+}
+
+std::vector<SpawnResult> Spawner::runCycle(SpawnEnvironment& env, SpawnCategory category,
+                                           const std::vector<Vec3i>& chunkColumns, uint64_t seed) {
+    std::vector<SpawnResult> results;
+    results.reserve(chunkColumns.size() * static_cast<std::size_t>(attemptsPerColumnCount));
+    for (const Vec3i& column : chunkColumns) {
+        for (int attempt = 0; attempt < attemptsPerColumnCount; ++attempt) {
+            results.push_back(runColumn(env, category, column, seed, attempt));
+        }
+    }
+    return results;
+}
+
+int Spawner::denialCount(SpawnDenial denial) const {
+    return denials[static_cast<std::size_t>(denial)];
+}
+
+void Spawner::resetStats() {
+    denials.fill(0);
+    spawned = 0;
+}
+
+std::vector<BehaviorAgent> agentsFromSpawn(const SpawnResult& result, uint32_t seed) {
+    std::vector<BehaviorAgent> agents;
+    if (!result.spawned) return agents;
+
+    const SpeciesStats& stats = speciesStats(result.species);
+    agents.reserve(result.positions.size());
+    uint32_t stream = seed != 0u ? seed : 0x9e3779b9u;
+    for (const Vec3& spot : result.positions) {
+        BehaviorAgent agent;
+        agent.species = result.species;
+        agent.position = spot;
+        agent.homePosition = spot;
+        agent.health = stats.maxHealth;
+        agent.maxHealth = stats.maxHealth;
+        agent.moveStep = stats.walkSpeed / static_cast<float>(ticksPerSecond);
+        agent.rng = behaviorNextRandom(stream);
+        agents.push_back(agent);
+    }
+    return agents;
+}
+
+} // namespace vf