With the release of Legend Nightmare Hunts, the Essence of Servitude is now available, and you'll need to find Ehrath'Ur's Horned Wreath to find it. Note that this is a separate item from the Horned Wreath found in the Chamber of Night, and that you don't actually need to play on Legend difficulty to receive the Essence of Servitude. With that out of the way, here's how to find the Destiny 2 Ehrath'Ur's Horned Wreath collectible.
How to find the Catacombs
The Catacombs is that long dark tunnel where you found the Hive glyph during Shadowkeep's campaign. To reach it in patrol mode, head to the Sorrow's Harbor landing zone in the northeast section of the Moon. Head southwest toward the Hellmouth, hugging the right wall until you reach a path leading downward. Keep descending, passing through the Gatehouse, until you reach the Circle of Bones.
From where you enter the Circle of Bones, the path to the Catacombs will be on your right side. Look for a large lantern on the right wall and go past it, not through the door below it. Hug the railing along the mouth of the Circle of Bones until you come to another hole in the wall on the right. Follow the GIF above if you get lost.
Once you're in the Catacombs, head down until you reach the first main chamber. As long as you have the Essence of Servitude on you, you'll find a unique yellow-bar Wizard named Malura, the Fated. Kill it and you'll receive Ehrath'Ur's Horned Wreath. Voila!
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