Sure, i first got the passage of Ma'Habre when I wa splaying as the Mercenary, thinking it was just the book Ma'Habere, I didn't think too much about it. When I realized it was a special book, I read it and I got transported to the Ancient City of Ma'Habere. The New Gods spoke to me about how I was gonna be chosen and stuff and i was on my way. I walked around and looted abunch of goodies from the urns and crates. Then I saw that creepy dead spider-person [I later was looking in local files and saw that apparently you can encounter a live one]. I didn't make it that far due to the time limit but I ended up looting those two chests, I did get it twice and just now when I'm playing too, well I usually always get it if I make the coin flip in one of the bookshelfs in the catacombs library, where I'm struggling to recruit the dark priest. Sometimes I belive pocketcat has it
Might be the same as the Altar of darkness - sacrificing party members to it gives nothing in return and praying to the God Of Depth gives no benefit either. Malevolent creatures don't really like to share, it seems. That makes me think - perhaps the Old Gods chose to be unresponsive to humans BECAUSE they stopped making actual requests to them and the new gods, while being presented as the heralds of salvation, provide no actual help at all as they have no wish to squander their newly acquired godly powers.
Also, thanks for the feedback, i'll make a mercenary and try to study the Ma'Habre's layout - I'll try to go deeper ignoring all the chests and barrels and see what it has to offer.