Nice Boss Room design. 100/100 (Zahmir, the Blade Sovereign)

https://steamcommunity.com/sharedfiles/filedetails/?id=3571209633

Before you is a room with a deadly boss on the Atlas map. If you've completed the interludes, you know that the boss event starts when you reach it on foot. While on foot, you can't use any abilities.

The room also contained two regular rare mobs and an active abyss with mobs and rares. They all attacked you with all their weapons while you were crawling on foot, while you couldn't use ANYTHING.

Could one of the developers comment on the design of this room and answer the question - what are the rare mobs doing there (I think this has already been removed by several patches) and the abyss itself?)