The Drow Summoning Ritual - Baldur's Gate 2 Side Quest
The Drow Summoning Ritual side quest begins after you hand Matron Mother Ardulace one of the 3 "blood" items that she asks for the first time you meet with her. You will meet her at the very end of the Inside The Drow City quest, technically this quest is a continuation of that one. Once you begin this side quest the Drow city of Ust Natha will become locked and no one will be allowed in or out of the city anymore.
Our first task at the start of this quest is to visit Phaere in the Female Fighter's Society once again. However, on the way to her you'll bump into a Drow by the name of Visaj who will ask you to buy a magical rope from him. You should buy this rope as it'll begin another side quest titled Intrigue with Jarlaxle which will net us some decent EXP and lots of magical items.
When you finally get to the Female Fighter's Society you'll be stopped yet again, this time by Taso Kala who will tell you to go to the southeastern most platform in the city and kill some people for her. This is actually part of the side quest Find the Worshippers of Ghaunadaur. After you complete this distraction return to Phaere and speak with her before she becomes impatient and this quest fails.
Phaere tells you that she wants to betray Matron Mother Ardulace and in order to do this you'll have to bring her the real pair of Adalon's Eggs from inside the Temple of Lolth. Now, if you left Solaufein alive earlier during the Inside The Drow City side quest then he will portal in as you approach the Temple of Lolth and offer you another pair of Fake Dragon Eggs.
You should take the pair of Fake Dragon Eggs from Solaufein which will give you a total of 2 fake eggs. We'll need both pairs of Fake Dragon Eggs to get the best outcome for this quest. Head inside of the Temple of Lolth and into the room in the northeast portion of the temple. A picture of exactly where this room is can be found below. There will be 2 guards outside of this room but they can be easily dispatched and no one in the city will care.
Inside the Egg Room you'll find a couple of Stone Golems that will turn hostile the moment you take the Dragon Eggs from the container. Much like with the Egg Guards, no one will really care if you smash the golems to pieces. While you're here you will have to decide how you want to finish this quest from here on out.
Depending on which route you'd like to go for the rest of this quest determines how you will want to proceed. You're going to have to place either the Fake Dragon Eggs (Solaufein) or Fake Dragon Eggs (Phaere) into the container and then report to either Matron Mother Ardulace or back to Phaere.
The best possible route for you to do is place the Fake Dragon Eggs (Phaere) into the container and then bring the Fake Dragon Eggs (Solaufein) to Phaere. You'll get the most EXP from going this route and you'll be able to bring untainted eggs to Adalon to complete the Recover the Silver Dragon's Eggs side quest for 78k EXP.
Additionally, if you're an Evil character you will be able to trade Adalon's Eggs yourself to the demon for a boon of some kind. The only reward the demon can give you that is even remotely worth it is Blackmist +4, a polearm which casts Blind up to 3 times a day. However, getting this polearm will cost you 78k EXP for every member of your party since you won't be able to turn in Adalon's Eggs for the reward. Plus it's a polearm which barely anyone uses.
Below you will find a list of all the different outcomes for this quest.
Betray Phaere: Tell Matron Mother Ardulace about Phaere's plans in the Temple of Lolth and she will demand 2 pairs of eggs from you as proof. You can give her Phaere's Fake Eggs and Solaufein's Fake Eggs and keep the real ones for yourself if desired. Keep in mind giving her Adalon's real eggs will result in the demon tainting them and you "failing" the Recover the Silver Dragon's Eggs side quest.
Work with Phaere: Place either Phaere's Fake Eggs or Solaufein's Fake Eggs into the container and then give the real eggs to Phaere.
Betray Phaere and Ardulace: This is the best route to go and the only route that will allow you to bargain with the demon and trade the eggs for a polearm. What you will want to do is place Fake Dragon Eggs (Phaere's) into the container and bring Fake Dragon Eggs (Solaufein's) to Phaere. Solaufein's eggs go into the container since Phaere will recognize her own fake eggs.
Once you make a decision on how to proceed and give someone a pair of Dragon Eggs you'll be notified that the ritual is starting and automatically be taken there. At the start of the ritual you'll have the opportunity of attacking Matron Mother Ardulace and Phaere; if they have the real eggs from Adalon then this is your last opportunity to get them before they become tainted.
There are a couple of different ways that this ritual can play out depending on your actions during the previous part. If either Phaere or Ardulace give the real Dragon Eggs to the demon he will taint the eggs and then expose who you are which will turn the entire city against you. Adalon's eggs being tainted means you will fail the Recover the Silver Dragon's Eggs side quest and lose 78k EXP for every character in your party.
As I said before, betraying both Ardulace and Phaere will get you the best outcome. Both Ardulace and Phaere will get killed by the demon when they try to give him fake eggs and you'll be able to loot everything they drop. Ardulace drops Gorgon Plate +4 along with a Ring of Spell Turning and Phaere drops the Drow Piwafwi Cloak that we gave her earlier.
When both of them are dead you'll have the opportunity to speak with the demon and depending on your alignment it'll be different. Evil characters are able to trade Adalon's Eggs to the demon for Blackmist +4, as I mentioned earlier. There are a few more options too, you can ask for safe passage out of Ust Natha and have the demon stampede through all of the Drow - taking all of your EXP. Or you can say pretty much anything else to the demon which will make him kill you.
Once the ritual is over it's time to exit Ust Natha. Technically you can escape right now without fighting anyone but I strongly recommend you buff up as much as possible and then fight your way out of the town. You'll get a ton of EXP for clearing out the entire town of Drow and it's a lot of fun so do it! Regardless of your choice, once the ritual is over that will conclude this quest.