I am still confused by the idea that the Priestess Gut must be killed anyway, if we want to get into the Underdark.
When I played the game for the first time, I thought that I would not be able to play for Minthara and the cult of the Absolute if I killed her, so I avoided dialogue about the tadpole, and in the end I did not get into the Underdark at all. Although on the second playthrough I killed the priestess Gut, found a true soul drow in the Underdark and helped him, he sent me to talk to Minthara about the journey to the Towers of Moonrise. It was in a dialogue with Minthara, but everyone forgot about the priestess Gut. This is good, because I would not want it to cause problems on the evil path, but I think the developers need to think about this point in more detail. Perhaps Minthara should say that the priestess of Gut is a fool and deserved her death as an option.
You don't really need the entrance in the Selune temple- there are lot's of other way to get to the Underdark - through the Whispering Depths, the Zentharim hideout, Auntie Ethels lair ... and I'm pretty sure, I miss some. I usually use the entrance in the Selune temple, because I kill everything in there anyway (apart from Abdirak and the goblin in the cage and of course Halsin, since he is the reason, I'm there anyway), but with featherfall Whispering Depths is a good alternative, just be aware, because you drop down near the minotaurs.
