I have tried learning Summon Quasit using the Wizard's ability to learn spells from scrolls and noted the following:
--- Only one of the scrolls allows learning the spell. Right-clicking on the other does not show the option.
--- If you don't already know Find Familiar, you do not get Summon Quasit, even if you later learn Find Familiar. May be deliberate.
--- If you don't have Find Familiar slotted when you use the scroll, you do not get Summon Quasit, even if you later slot Find Famliar.
--- One of the new changes is: "In the Thayan Cellar, skeletons now destroy their caskets when spawning." The scrolls are found in the caskets and destroying containers destroys their inventory. So normal gameplay may make getting the scrolls impossible. May be deliberate but it is irritating to lose important items due to scripted actions.
The last has a workaround:
1. Ungroup all of your characters. Set up their positions to block off the area around the casket closest to the mirror. You should be able to completely block ground movement from that area to other areas by standing in the narrow areas on two sides. It helps if you have a summons or two.
2. Open the casket. It will get a surprise round and open the next closest casket (I haven't found a way around that). You will now have two enemies: an archer stuck in the middle of your group and a melee just outside your group.
3. Kill the melee before it can move to another casket. It has high AC and high HP, so a combination of Magic Missile, area attacks, and positioning for attacks of opportunity is necessary. You must also kill the archer before it can get to another casket, but it is in an enclosure (unless you move your characters too much).
This will break the chain - no other enemies spawn when you open the other caskets. This might be unintended, but it works.
