It took us over 20 wipes during last 2 weeks and 2 raid extends. We've spent at least 5 hours learning this fight phase by phase. Mastering every phase and transitions was crucial. Our healers did great job in dispelling and healing, our damage dealers did great job on downing Spirits quickly and awesome job on killing Vile Spirits in phase 5. Everyone was focused and passing Necrotic Plague on Horros was going without problems. Tanks, well, just didn't do anything stupid, so it was a success :D Defiles were always placed properly away from center of the room. We rotated stuns and slowing effects on Val'kyries. Simply put, great job everyone! :D Well deserved achievement!
PS. and who says that Hero is mandatory buff? ;)