Corla , Herald of Twilight " Formerly an accomplished Kirin Tor mage , Corla now serves the Twilight ' s Hammer with unwavering devotion . She blesses fellow by harnessing nether dragon essences to transform these believers into menacing . " Corla , Herald of Twilight is the second boss of Blackrock Caverns . She and many of her fellow zealots can be found within the Halls of Awakening , midway through the Caverns . Strategy . Corla has three adds in front of her called Zealots . While they are praying in front of her they are harmless . However , you will notice before the boss is pulled that there is a beam of purple light being channeled from the purple dragon at the top of the room to the zealots . The " beam of purple light " is the key mechanic to this fight . Once the tank pulls , the beam of purple light will begin to transform each of the 3 adds into an EVOLVED twilight zealot . When a zealot evolves it is now lethal and deals massive amounts of damage to the tank . However , if a player stands in the way of the beam the zealot will NOT transform into its evolved form . While a party member is standing in the beam they will gain a stacking debuff , which builds rather quickly . If the debuff reaches 100 , the player standing in the beam will become mind controlled and will turn on their own party members as an enemy ( therefore leading to a wipe ) . Mark two zealots , one with a SKULL and one with a CROSS ( or any raid markers really ) . Whichever two zealots you choose to mark , you should mark them right next to each other . Never mark the far left and far right zealots together , ALWAYS MARK THE MIDDLE ZEALOT and either the far left OR far right The UNMARKED zealot will never have a party member in front of it , and therefore you will INTENTIONALLY let that zealot transform . The tank will pull the boss , and be ready to pick up the EVOLVED zealot when the normal zealot transforms . That said , the boss can be killed WITHOUT ANY OF THE THREE ZEALOTS TRANSFORMING . All three zealot beams can be blocked by players using one of the strategies below ; the adds despawn when the boss dies . This strategy is particularly effective for ranged - dps heavy groups and / or groups where the healer struggles to keep the tank up with boss + one transformed zealot . The other 4 party members will have to divide into 2 groups of 2 . Each group gets assigned one zealot to prevent them from transforming . One person in each group will stand in the beam ( thus preventing the transformation ) until their debuff gets to 70 or 80 stacks . Then , that person will move out of the beam and switch places with the other member of their group . Both groups keep alternating who is standing in the beam to prevent two zealots from transforming . It is important to note that the dps must continue to dps , and the healer must continue to heal while in the beam . Your tank can be in one of your groups , but it can be tricky for the tank to pick up the first zealot after it transforms , tank the boss , and try not to get mind controlled from standing in the beam too long . It ' s much easier for the healer to just focus on healing and move out of the beam . Let the tank hold aggro on the boss , pick up evolved zealots , then position the boss and zealots . The tank should position the boss in between the two marked zealots , so that any melee dps in the beam groups can continue to dps . After a zealot transforms , once again the tank should pull the EVOLVED zealot and the boss within range of the rest of the party . If the tank was a part of a group , when it was the tank ' s turn to stand in the beam , he may not be able to position the boss and adds in such a way that everyone can be in range to dps them . After you down the first EVOLVED zealot , you ' re now going to focus on the zealot you marked with a skull . Whatever group was on the skull will stop standing in the beam . Now the tank will pick up the skull zealot after it transforms . Remember , the party must switch and quickly dps down any EVOLVED zealots . Whenever , an evolved zealot is not up , the group should just focus dps on the boss . After killing the skull zealot , only the cross zealot should be left . Now the group responsible for the cross zealot moves out of the beam , lets that zealot become EVOLVED , the tank picks up the cross EVOLVED zealot , and the group focuses dps on the evolved zealot . After downing all THREE EVOLVED zealots , you just dps down the boss . Alternate Strat : Debuff Swap . In many ways this fight is a scaled down version of the Netherspite encounter from Karazan . In normal mode the stacking " MC Debuff " falls off after 10 seconds , 14 seconds in heroic mode . So , the easiest way to handle this fight is to have the tank hold the boss near , but not in one of the beams . Near enough to the beam that a melee DPS in the beam can reach her however . 2 DPS ( preferably your melee ) are assigned to this closer beam . 1 DPS ( preferably ranged ) and your healer are assigned to the further beam . The two players alternate their time in the beam , step out when you reach ~ 80 stacks and let your partner step in . Once your debuff falls off , step back in . The evolved debuff appears to fall off the zealots as well , so the occasional few ticks hitting them isn ' t fatal . Classes that have immunity spells ( paladin bubble , mage ice block etc . ) can also use it while standing in the beams . The beam will not flip back to the zealot , it will simply keep ticking on the player giving an immune reaction . This also clears the stacks already on the player . ( Tested with mage ice block , assumed to work with other immunity effects as well ) . Done properly , neither zealot ever evolves and the tank need only cope with the boss herself . Alternate Strat : The Distinct Lack of Fail Swap . If the other strategies seem too ridiculous to contemplate : they are . Corla ' s Dark Command is interruptable . There is never a reason why anybody should be feared from a beam except latency or failure . One important thing to remember : THE BOSS CAN BE KILLED WITHOUT NEEDING TO KILL ANY ADDS . Healer can take one beam , a ranged can take the second and the tank take the middle . Alternatively if you have two ranged DPS in addition to the healer , each of these players can take one beam to interrupt . If you are melee heavy , the tank has ~ 10 seconds at the beginning of the encounter to position the boss so she ' s attackable from both sides of one Zealot . A convenient way of managing beams is to stand in the beam next to the Zealot , when you hit 80 stacks , strafe through the zealot as the beam will more quickly switch to him . Strafe back when your stacks are off ( 10 sec on regular , 14 sec on heroic ) . You only have to move about 3 - 4 yards . This rotation can be done as long as needed , as noted earlier the stacks seem to cool off the adds as well . Setting yourself as your focus may help you keep track of your stacks and when they fall off . If you can ' t see your debuffs , consider something like BigDebuffs on XPerl . By carefully managing all three adds and never allowing any to transform , this boss is easy , especially for range dps - heavy groups .