Ir Yût, the Deathsinger

Ir Yût, the Deathsinger is a Hive Wizard found in Crota's End. She is found in the final chamber of the Raid, and must be killed before Crota can be summoned. 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.

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.

Trivia

 * Despite her being killed in the raid she can still be found in the mission lost to light which takes place after the Crota's End raid.