Hello, we did yesterday BWL with the Black trial. Sadly every Boss in the Dungeon is loged as mythic mode buf nefarian is loged as Heroic.
Here a link to the log: Report: 2024/09/29 - BWL Nef | Warcraft Logs Season of Discovery
we also get the bigger reward for the black trial in addition to Shadowflame items. Also you can see that the 3 debuffs was applyed to the players.