The Deathbringer Rocket Launcher is one of the powerful new exotic weapons introduced in Destiny 2 with the release of the Shadowkeep expansion. After completing the main story campaign, talk to Eris Morn and take the quest "Memory of Sai Mota".
Step 1: complete the three Lost Sectors
First thing you need to do is walk three Lost Sector on the Moonwho are NOT in Sorrow's Haven:
Step 2: transfer the Firewall chunk
As a result, you will receive a piece of firewall data, which needs to be transferred to the Revelation K1 sector. Once you defeat the boss, go to the system kernel storage on the right side and use the fragment to open the door. You will receive the quest "Sai Mota's Broken Necklace" in which you need to find the Necklace Shards.
Step 3: collect the necklace shards
You have to kill nightmares on the moon with the lightning abilities. I recommend heading to the Harbor of Sorrow area, as there are many nightmares that are constantly reviving. Once you have collected 20 shards, use the portal and return to Eris Morn in the Hideout.
Take the reward from the box at Eris' site in the Enduring Abyss, and then talk to Eris Morn and take another quest - "Symphony of Death".
Step 4: find the Skull of Silence
Travel to the Circle of Bones marked on the map in the Hellmouth region. It's underground, so go through the large door in the Archer's Line and follow the tunnels through the Hall of Wisdom. The entrance to the Circle of Bones is located in the east of the area - a door with a green light.
After obtaining the Skull of Silence, return to Eris Morn and talk to her.
Step 5: collect the bones
You will receive a new quest in which you need to find: a ritual bone in the Revelation K1 sector, a festering bone in a public event near Hell's Mouth, and the bone marrow of a Bone Collector named Acolyte. It spawns randomly in the Anchor of Light.
Step 6: kill the Supreme Conductor
Start the Scarlet Fortress raid and head to the second floor in the room to the left of the elevator leading to the boss. Jump off the lift as soon as it starts to climb and start killing adds until you teleport.
Step 7: complete the quest "Harmony of Darkness"
You need to kill 10 bosses, 72 mini-bosses and 300 regular enemies on the moon. Bosses can be farmed in Sorrow's Harbor, and Escalation Protocol on Mars is recommended for elite opponents and mini-bosses.
Step 8: complete the Chorus of the Damned quest
Travel to the Circle of Bones using the route described above. The recommended level for the quest is 920, but if you are playing in a team, 900 will do.
You must survive the "Song of Death" sung by the Death Singer Ir Absul at random intervals. This gives you a minute timer, and if during this time you are unable to break through the shields and stop chanting, Ir Absul will destroy you. In addition, you have to defend against a large number of enemies.
Once you kill the boss, return to Eris Morn and take the rocket launcher from her.
