diff --git a/core/src/Boss.cpp b/core/src/Boss.cpp
index 84bc50e..6790e7d 100644
--- a/core/src/Boss.cpp
+++ b/core/src/Boss.cpp
@@ -154,3 +154,163 @@ DragonFight::DragonFight(const EndGenerator& end, uint32_t seed, const DragonFig
     portal = {0.5f, static_cast<float>(surface), 0.5f};
     eggCell = {0, surface + 1, 0};
 
+    boss.position = portal + Vec3{cfg.orbitRadius, cfg.orbitHeight, 0.0f};
+    ctx.rng = boss.rng;
+    buildTree();
+}
+
+int DragonFight::aliveCrystalCount() const {
+    int total = 0;
+    for (const CrystalNode& crystal : pillarCrystals) {
+        if (crystal.alive) ++total;
+    }
+    return total;
+}
+
+void DragonFight::buildTree() {
+    auto death = seq("deathThroes");
+    death->add(cond("healthGone", [this](BehaviorContext&) { return boss.health <= 0.0f; }));
+    death->add(act("collapse", [this](BehaviorContext&) {
+        if (boss.phase != BossPhase::Dying) {
+            boss.enterPhase(BossPhase::Dying);
+            return BehaviorStatus::Running;
+        }
+        if (boss.phaseTicks < cfg.deathTicks) return BehaviorStatus::Running;
+        boss.enterPhase(BossPhase::Defeated);
+        boss.alive = false;
+        boss.bar.visible = false;
+        boss.bar.setFromHealth(0.0f, boss.maxHealth);
+        portalOpen = true;
+        eggDropped = true;
+        return BehaviorStatus::Success;
+    }));
+
+    auto volley = std::unique_ptr<ParallelNode>(new ParallelNode("perchAssault", 1, 2));
+    volley->add(gated("breathCooldown",
+                      act("breatheAcid",
+                          [this](BehaviorContext& context) {
+                              if (!context.playerPresent) return BehaviorStatus::Failure;
+                              if (distanceBetween(boss.position, context.playerPosition) >
+                                  cfg.breathRange) {
+                                  return BehaviorStatus::Failure;
+                              }
+                              damageThisTick += cfg.breathDamage;
+                              ++boss.attacksLaunched;
+                              return BehaviorStatus::Success;
+                          }),
+                      cfg.breathCooldownTicks));
+    volley->add(gated("swipeCooldown",
+                      act("tailSwipe",
+                          [this](BehaviorContext& context) {
+                              if (!context.playerPresent) return BehaviorStatus::Failure;
+                              if (distanceBetween(boss.position, context.playerPosition) >
+                                  cfg.swipeRange) {
+                                  return BehaviorStatus::Failure;
+                              }
+                              damageThisTick += cfg.swipeDamage;
+                              ++boss.attacksLaunched;
+                              return BehaviorStatus::Success;
+                          }),
+                      cfg.swipeCooldownTicks));
+
+    auto perchAction = sel("perchAction");
+    perchAction->add(std::move(volley));
+    perchAction->add(act("holdPerch", [](BehaviorContext&) { return BehaviorStatus::Success; }));
+
+    auto perch = seq("perchAtPortal");
+    perch->add(cond("allCrystalsDown",
+                    [this](BehaviorContext&) { return aliveCrystalCount() == 0; }));
+    perch->add(act("descendToPortal", [this](BehaviorContext&) {
+        boss.enterPhase(BossPhase::Perching);
+        Vec3 landing = portal + Vec3{0.0f, cfg.perchHeight, 0.0f};
+        Vec3 delta = landing - boss.position;
+        float span = length(delta);
+        if (span <= cfg.perchDescentStep) {
+            boss.position = landing;
+            return BehaviorStatus::Success;
+        }
+        boss.position += delta * (cfg.perchDescentStep / span);
+        return BehaviorStatus::Running;
+    }));
+    perch->add(std::move(perchAction));
+
+    auto charge = seq("chargePlayer");
+    charge->add(cond("playerWorthCharging", [this](BehaviorContext& context) {
+        return context.playerPresent &&
+               distanceBetween(boss.position, context.playerPosition) <= cfg.chargeTrigger;
+    }));
+    charge->add(gated("chargeCooldown",
+                      bounded("chargeWindow",
+                              act("charge",
+                                  [this](BehaviorContext& context) {
+                                      if (!context.playerPresent) return BehaviorStatus::Failure;
+                                      boss.enterPhase(BossPhase::Charging);
+                                      Vec3 delta = context.playerPosition - boss.position;
+                                      float span = length(delta);
+                                      if (span <= cfg.chargeContactRange) {
+                                          damageThisTick += cfg.chargeDamage;
+                                          ++boss.attacksLaunched;
+                                          return BehaviorStatus::Success;
+                                      }
+                                      boss.position += delta * (cfg.chargeSpeed / span);
+                                      return BehaviorStatus::Running;
+                                  }),
+                              cfg.chargeWindowTicks),
+                      cfg.chargeCooldownTicks));
+
+    auto breath = seq("acidBreath");
+    breath->add(cond("playerNearPortal", [this](BehaviorContext& context) {
+        return context.playerPresent &&
+               distanceBetween(context.playerPosition, portal) <= cfg.breathRange;
+    }));
+    breath->add(gated("flightBreathCooldown",
+                      act("breatheFromAbove",
+                          [this](BehaviorContext&) {
+                              boss.enterPhase(BossPhase::Breathing);
+                              damageThisTick += cfg.breathDamage;
+                              ++boss.attacksLaunched;
+                              return BehaviorStatus::Success;
+                          }),
+                      cfg.breathCooldownTicks));
+
+    auto root = sel("dragonRoot");
+    root->add(std::move(death));
+    root->add(std::move(perch));
+    root->add(std::move(charge));
+    root->add(std::move(breath));
+    root->add(act("orbit", [this](BehaviorContext&) {
+        boss.enterPhase(BossPhase::Circling);
+        boss.orbitAngle += cfg.orbitStep;
+        if (boss.orbitAngle >= fullTurn) boss.orbitAngle -= fullTurn;
+        boss.position = portal + Vec3{std::cos(boss.orbitAngle) * cfg.orbitRadius, cfg.orbitHeight,
+                                      std::sin(boss.orbitAngle) * cfg.orbitRadius};
+        boss.heading = normalize(Vec3{-std::sin(boss.orbitAngle), 0.0f, std::cos(boss.orbitAngle)});
+        return BehaviorStatus::Success;
+    }));
+
+    tree.setRoot(std::move(root));
+}
+
+int DragonFight::resolvePlayerShot(const DragonPlayerInput& input) {
+    if (input.shootCrystal < 0) return 0;
+    if (input.shootCrystal >= static_cast<int>(pillarCrystals.size())) return 0;
+
+    CrystalNode& crystal = pillarCrystals[static_cast<std::size_t>(input.shootCrystal)];
+    if (!crystal.alive) return 0;
+    if (crystal.cageIntact) {
+        if (input.breakCage) crystal.cageIntact = false;
+        return 0;
+    }
+
+    crystal.alive = false;
+    crystal.health = 0.0f;
+    crystal.destroyedTick = boss.tick;
+
+    if (distanceBetween(crystalCenter(crystal.position), boss.position) <= cfg.crystalBlastRange) {
+        float dealt = std::min(cfg.crystalBlastDamage, boss.health);
+        boss.health -= dealt;
+        boss.damageTaken += dealt;
+    }
+    return 1;
+}
+