diff --git a/src/server/scripts/Northrend/Ulduar/Ulduar/boss_yoggsaron.cpp b/src/server/scripts/Northrend/Ulduar/Ulduar/boss_yoggsaron.cpp
index dff9c61ca..08835f46c 100644
--- a/src/server/scripts/Northrend/Ulduar/Ulduar/boss_yoggsaron.cpp
+++ b/src/server/scripts/Northrend/Ulduar/Ulduar/boss_yoggsaron.cpp
@@ -469,7 +469,7 @@ struct boss_yoggsaron_sara : public ScriptedAI
         {
             _instance->DoStopTimedAchievement(ACHIEVEMENT_TIMED_TYPE_EVENT, CRITERIA_NOT_GETTING_OLDER);
             _instance->DoRemoveAurasDueToSpellOnPlayers(SPELL_SANITY);
-            _instance->SetData(BOSS_YOGGSARON, NOT_STARTED);
+            _instance->SetBossState(BOSS_YOGGSARON, NOT_STARTED);
             if (GameObject* go = _instance->GetGameObject(DATA_YOGG_SARON_DOORS))
                 go->SetGoState(GO_STATE_ACTIVE);
         }
@@ -480,12 +480,11 @@ struct boss_yoggsaron_sara : public ScriptedAI
         if (!_instance)
             return;
 
-        // some simple hack checks
-        if (_instance->GetBossState(BOSS_VEZAX) != DONE || _instance->GetBossState(BOSS_XT002) != DONE)
+        if (_instance->GetBossState(BOSS_VEZAX) != DONE)
             return;
 
         _instance->DoStartTimedAchievement(ACHIEVEMENT_TIMED_TYPE_EVENT, CRITERIA_NOT_GETTING_OLDER);
-        _instance->SetData(BOSS_YOGGSARON, IN_PROGRESS);
+        _instance->SetBossState(BOSS_YOGGSARON, IN_PROGRESS);
         me->SetInCombatWithZone();
         AttackStart(target);
 
@@ -702,6 +701,14 @@ struct boss_yoggsaron_sara : public ScriptedAI
 
     void DamageTaken(Unit* who, uint32& damage, DamageEffectType, SpellSchoolMask) override
     {
+        // Guardians can be spawned by walking into Ominous Clouds even when InitFight
+        // never ran (e.g. Vezax not defeated); their novas must not start phase 2 then.
+        if (!_instance || _instance->GetBossState(BOSS_YOGGSARON) != IN_PROGRESS)
+        {
+            damage = 0;
+            return;
+        }
+
         if (who && who->GetEntry() == NPC_GUARDIAN_OF_YS && !_secondPhase)
         {
             damage = 25000;
@@ -1104,7 +1111,7 @@ struct boss_yoggsaron : public ScriptedAI
 
         if (_instance)
         {
-            _instance->SetData(BOSS_YOGGSARON, DONE);
+            _instance->SetBossState(BOSS_YOGGSARON, DONE);
             if (Creature* sara = _instance->GetCreature(DATA_SARA))
                 sara->AI()->DoAction(ACTION_YOGG_SARON_DEATH);
             if (GameObject* go = _instance->GetGameObject(DATA_YOGG_SARON_DOORS))
diff --git a/src/server/scripts/Northrend/Ulduar/Ulduar/instance_ulduar.cpp b/src/server/scripts/Northrend/Ulduar/Ulduar/instance_ulduar.cpp
index 9daa556ff..4cdd6bc11 100644
--- a/src/server/scripts/Northrend/Ulduar/Ulduar/instance_ulduar.cpp
+++ b/src/server/scripts/Northrend/Ulduar/Ulduar/instance_ulduar.cpp
@@ -47,7 +47,8 @@ DoorData const doorData[] =
     { GO_KEEPERS_GATE,                 BOSS_THORIM,    DOOR_TYPE_PASSAGE    },
     { GO_KEEPERS_GATE,                 BOSS_FREYA,     DOOR_TYPE_PASSAGE    },
     { GO_VEZAX_DOOR,                   BOSS_VEZAX,     DOOR_TYPE_PASSAGE    },
-    { GO_YOGG_SARON_DOORS,             BOSS_YOGGSARON, DOOR_TYPE_ROOM       },
+    // GO_YOGG_SARON_DOORS is handled by boss_yoggsaron_sara: it closes 15 seconds
+    // after the pull, not immediately when the encounter enters IN_PROGRESS.
     { GO_DOODAD_UL_SIGILDOOR_03,       BOSS_ALGALON,   DOOR_TYPE_ROOM       },
     { GO_DOODAD_UL_UNIVERSEFLOOR_01,   BOSS_ALGALON,   DOOR_TYPE_ROOM       },
     { GO_DOODAD_UL_UNIVERSEFLOOR_02,   BOSS_ALGALON,   DOOR_TYPE_SPAWN_HOLE },