Ir Yût, the Deathsinger
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Ir Yût, the Deathsinger is a Hive Wizard Deathsinger found in Crota's End. She is found in the final chamber of the Raid, and must be killed before Crota can be summoned. Toland, the Shattered was quite interested in her Deathsong, trying to figure out how she could sing it without dying. He speculated that she made herself part of the song, and became death incarnate.
Unlike all the other raid bosses before her, Ir Yût will not immediately be actively attacking any Guardians. Instead, she will have locked herself inside the room containing Crota's summoning crystal. At this time, all players should be focused on killing enemies, namely Shriekers. Once they are destroyed, she will activate her special ability.
Ir Yût is an especially dangerous wizard, as her special power is the Deathsong, which kills anyone who hears it when it is complete. She will start the song once any Guardians are detected, in which they will have three minutes to kill her before she completes it. There will be a countdown for the last 30 seconds of this song, which is when the barrier will be unlocked, allowing the player to unleash all damage on her as possible.
Age of Triumph added a Challenge Mode for Ir Yût. In order to complete it, the players must kill everything in the area (including the Wizards and Shriekers) and then kill her with an Ascendant Sword. Once the first wave of enemies are killed, a message saying "Ir Yût shrieks in fear" will appear on the bottom left. The fireteam must rush into the open area and kill everything (including Ogres) once more to spawn a Swordbearer. Once it is killed, a Guardian must pick up the sword and rush back to Ir Yût and kill her with one swipe.