The problem is that sometimes the masks turn neutral at the end of the fight, after Ethel is dead, and sometimes they don’t. I have not found a pattern to this. I thought it might be tied to Ethel getting in her surrender speech but that’s not it. It makes no sense to me that the behaviour isn’t consistent, and that even if they do stay hostile you can flee and come back and they are neutral.
I understand that. Hint: I did it this way, and that alone was very lucky that I was able to beat up the Hag enough in the first round to force her to give up in the second. Otherwise, the fight gets really tough. In her first round, she sets the cage on fire and calls for the masks. From the second round on, she calls her clones. A bit witless when a party of four faces four clones and gets incapacitated (Hold Person) by them and then leisurely taken apart by four masks + Vettel without being able to fight back. And even then you had a ranged hit chance between 25 -36 % and I was not really far away from the Vettel or her closest clones... If that's supposed to be the default difficulty, then I don't know how the higher difficulty levels are supposed to turn out. Anyway, I managed it with my LEVEL 4 party with a lot of luck, so that really only the stupid Vettel died...
It was probably set up so that the Vettel would only be confronted with level 5. On the other hand, if everyone is permanently affected by Hold Person, then you can also be level 10 and watch yourself die. Just kidding, the saving throws should be better from a higher level.
But to me, it seems illogical to reach level 5 by entering the Underdark first, because that means you also enter the Goblin Camp, and if you make a wrong decision here, you can quickly find yourself defending the Druid Grove and losing the opportunity to confront Kagha as a Shadow Druid, for example. Of course, you could go into the swamp beforehand and seek out the Vettel much later, but that's illogical exploration. I'm not going to meet the Vettel and Mayrina's brothers in the swamp. Explore the swamp only half-heartedly and leave Mayrina to the Vettel indefinitely, just because I'm going to the Underdark to become level 5 and face her with more combat power.
However, I have reported more than enough inconsistencies in the whole Auntie Ethel Arc. Also serious bugs. For example, if you refuse to give Mayrina the wand or kill her Zombie husband, she becomes hostile and the masks that are still in Hag's lair become hostile and the camera suddenly zooms to the masks even though your party is outside with Mayrina...
I speculate that you may not harm the masks at all, nor Mayrina + husband, or they will still be hostile after the Vettel's death, or become so again.
All in all, I'd prefer to have a reasonable implemented non-lethal attack option in the game so that knocked out individuals are amenable at a later point in time and aren't just considered dead.
