History of Blooming Deep Solo Mastery

Blooming Deep Solo Mastery is a triumph: complete the Blooming Deep on Master difficulty without a fireteam. It is a Lost Sector in The Blooming area of The Pale Heart (The Blooming Deep).

How to complete

1. Find the entrance in The Blooming: search the southern edges for a cave entrance marked by the Lost Sector symbol near a ledge with thick vines hanging down; use the vines to guide you and jump up (Prima Games / Escapist summaries).
2. Expect mostly Taken with some Dread; the boss is Azshrunah ur-Nokru the Sacrificed, a Taken Knight. The sector has Champions (Overload and Unstoppable per the in-game text).
3. Launch it alone on Master. Deaths are allowed here; the flawless version requires none.
4. Bring weapons effective against Taken and Hive-style shields, and be patient with the platforming.
5. Beware Taken Phalanxes near platform edges; their shield blast can knock you off.

Unconfirmed

Seal and reward were not found in sources I opened, and no exact loadout is confirmed. The linked video shows a solo flawless Master run on Titan.