Dwarves of Dumathoin

Dwarves of Dumathoin is a quest in Baldur's Gate: Siege of Dragonspear, available starting in Coast Way Crossing during chapter eight.
This is one of the longer, more involved quests in the expansion. The goal of this quest is to rescue a group of dwarven clerics from an infestation of undead in the Dwarven Dig Site, and then determine how to deal with darker secrets dwelling below.
==Walkthrough==
=== Rescuing the dwarven clerics ===
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=== Saving Semahl ===
Traveling directly north at the first opportunity, the party will encounter the giant Semahl under attack by a Cold Wight, two Ghasts, a Wight, and a Wraith.
Saving him from death and not triggering a combat in the following conversation will earn the party .
=== Exploring the Dwarven Dig Site ===
Once past the entrance of dig, the mine splits vertically into four corridors and the locations of note are:
* the chamber to the north that contains a chest locked by a special key that has 
* the second north-most branch which leads to Crommus's secret stash containing the Bard Hat, the Crommus's Capelet, the Star-Strewn Boots, and the Tangled Strings
* the third north-most branch which dead ends in the exit to Repository of Undeath.
===Exploring the Repository of Undeath===
There are many undead in the repository, plan accordingly. Collect three scepters throughout the dungeon and the white potion.  These are placed in the large pool near the beginning of the level. You may then watch three cut scenes giving you more backstory on three different characters. Doing so awards to each party member for each cutscene.
There are at least two rooms to the northeast with quite a few undead. Be ready with AOE firebombs, slow spells, etc. 
The last room to the north has four pillars with a plaque describing different seasons (from left to right: autumn [cracked leaf], spring [leaf], winter [snowflake], summer [shining sun]). Interact with each of the pillars twice in this order: winter (3), autumn (1), summer (4), spring (2).Nature's order of life is spring, summer, autumn and, lastly, winter. The puzzle is an analogy of Lichdom: "For inherent in undeath, and particularly in the state of Lichdom, is a reversal of nature's order. The winter that is the end of mortal life is a rebirth for the undead. The autumnal deterioration of life energy that precedes the mortal winter follows the rebirth in undeath, as the fragmenting of mind and body are sewn back together, resulting in a period of illumination during which the undead sees the world in all its brilliant facets. Finally, there is the Lich's spring, a season of growing power and vitality that can and will be sustained for an eternity, so long as their phylactery and physical vessel endure." (A Philosophical Treatise on the Nature of Lichdom) If you press one of the plaques out of order, some mephits will spawn (lightning, earth, cold or fire) and the puzzle will reset. 
Successfully solving the puzzle opens the nearby door to find Gurn Coldhearth. 
Perhaps sensing his own vulnerability as a freshly-born lich, Gurn Coldhearth is surprisingly open to conversation. As long as you do not directly threaten him in dialogue, he will ask you to bring him the five Amulets of the Keeper of Secrets Under the Mountain from the dwarves in the dig site above, and promises an item of great power. If you already have at least one of these amulets but not all five, do NOT show it to him, as he will say you're trying to cheat him and attack. Agreeing to help him will not commit you to any particular path.
If you detect the secret door on the north side of his chamber, pick the lock, and open it, Gurn will immediately turn hostile towards you, so you may wish to avoid this unless you are prepared to fight him.
At this point, you have a choice to make in how to proceed.
====Siding with Gurn Coldhearth====
Should you decide to side with Gurn, the most straightforward way to complete the quest is to return to the Dwarven Dig Site and kill Brother Deepvein and his fellow dwarven clerics. If you saved Semahl earlier you will have to fight him as well. Likewise if you informed Daran Highhammer that his employers were still alive inside he will join the battle.
Killing them is easier said than done, as a group of this many divine casters at once is a force to be reckoned with, with many buffs, debuffs and even damaging spells flying around at once. After they are dead, search through their possessions for three of the amulets (dropped by Deepvein and two of the unnamed clerics).
Alternatively, a rogue may pickpocket the amulets from the dwarves to avoid a fight and also keep your options open for who to assist in this quest.
The other two amulets are easy to find on your first visit to the dig site and it is likely you will already have them. One is found on the ground near Brother Deepvein and the other is in the far southeastern room (an encounter with umber hulks).
Return to Gurn and give him the amulets. Your potential rewards are heavily influenced by your dialogue choices here:
* Saying anything other than "I'm happy you're happy" will result in Gurn giving you the Dread Hammer +2. Additionally in the following dialogue choice, saying "You'd best be right about that--for your sake" will result in the same reward.
* Mentioning the threat of Caelar will get you the promise of Gurn's aid in the battle against her, and no other reward.
* Saying "These weren't easy to get" begins a more complicated set of options. You can ask for either of the rewards mentioned above, or you can ask for everything you were promised and more. Doing so when Gorion's Ward has less than 18 strength will result in Gurn attacking you. With 18 or more strength, he will be annoyed by your greed and will give you one more chance to ask for either of the two rewards. You may dispute this again and demand both rewards, and this time if Gorion's Ward has less than 18 charisma Gurn will attack. With 18 or more charisma, he will be impressed by your bold display of avarice and will grant you both rewards, the hammer and his assistance against Caelar.
* Under all circumstances above, if Edwin Odesseiron is in the party when you receive only the hammer, he will speak up and also convince Gurn to provide aid in the upcoming battle against Caelar Argent. This does not apply in reverse -- if you only ask for help against Caelar, that is all you will receive.
====Siding with the dwarven clerics====
Should you decide to side with Deepvein and the clerics, return to them up at the dig site and tell Brother Deepvein the truth about Gurn. Deepvein will need to be convinced that his friend has betrayed him and become a creature of darkness.
* If you simply tell him that Gurn is now a lich and Gorion's Ward has less than 9 charisma, he will insist you are lying and attack. With 9 or more charisma he will accept what you tell him.
* If you are rude to him he may exit conversation.
* As a Cleric, a non-Blackguard Paladin, or a fellow dwarf he will automatically believe you.
* If you retrieved the Journal of Gurn Coldhearth from his chest, you can show it to Deepvein to prove it to him. If you mention the journal but refuse to show it to him, he may attack (but will give you one more chance to show it to him if Gorion's Ward is a dwarf).
* In all circumstances, if Semahl is alive he will back you up, stating that Gurn hurt him when no one else was looking and told him not to tell the others, which will convince Deepvein.
* If you have already destroyed Gurn and tell him Gurn was a lich and he is dead, in some cases it will be more difficult to convince Deepvein of what you are saying. The charisma requirement may increase to 11. Depending on the way dialogue goes he will believe fellow dwarves but potentially not Clerics and Paladins, instead attacking them on the spot. He will also attack you if you are dismissive, rude, or try to show him Gurn's remains. As before, Semahl will convince him regardless of anything else.
If Brother Deepvein is convinced he will ask for your help in destroying his former friend and will give you The Secret Revealed, a usable gem that is specifically designed to weaken liches. You may use it three times before its power is depleted, but Deepvein can recharge it for you twice more before it's unusable. However, you will not be able to recharge it while Gurn is still a threat, as a wall of force will prevent you from leaving the Repository of Undeath as long as he is hostile to you. The battle will be to the death.
Return to the Repository of Undeath to confront Gurn Coldhearth.
Gurn is an extremely powerful combatant, with access to many spells your party will not be able to cast until well into later games, spells you will never have even seen before at this stage of the game. He will cast Chain Contingency triggering Protection From Energy, Protection From Magical Weapons, and Spell Shield. He also has a regular Contingency set up that will trigger Stoneskin. He can cast 9th level spells such as Time Stop and Power Word, Kill, and many other powerful spells such as Abi-Dalzim's Horrid Wilting, Ruby Ray of Reversal, Power Word, Stun and Finger of Death.
It is possible to kill him without any special advantages, but the battle is much easier with the use of The Secret Revealed, which permanently removes many of his immunities and resistances, dispels any protections he has up, causes him to miscast magic and deals a bit of damage (see The Secret Revealed (spell) for details). You should be able to kill Gurn with the help of only one or two uses.
The moment Gurn dies, you have about one minute of real time to find and destroy his phylactery before he revives again at full strength and teleports to your location in the Repository of Undeath. As such you will need to hurry through the following steps.
When Gurn is killed he will drop the Ancient Key which will open the secret door on the north side of his chamber (if your thief has not already picked the lock). At the end of the long hallway is a chamber with six phylacteries. Interacting twice with the fourth from the left will get you two Black Opals, and the fifth from the left will get you a Diamond. The rest drop nothing, except Gurn's which is the second from the left. Interact with it twice to remove it.
Next you will need to destroy the phylactery, which can only be done using the energies of the Elemental Plane of Fire (where the box was forged), conveniently accessible via the magic circle on the far west side of the Repository of Undeath. You may have an easier time doing this before Gurn rematerializes if you use one character as a dedicated runner, especially with The Paws of the Cheetah equipped and/or Haste cast. Make your way to the circle as quickly as you can. It is likely that more fire-based monsters will have appeared within the circle since you last visited, but it is possible to ignore them momentarily for the real purpose you are here. Interact with the center of the circle to cast the golden box into the flames, destroying the lich Gurn Coldhearth once and for all. For doing so you will earn 3000 quest XP for each party member, an Emerald, a King's Tears, , and an additional 22,000 XP.
Return to Brother Deepvein and let him know that Coldhearth is no more. He will reward you with a scroll of Greater Restoration and the Helmet of Dumathoin. You will also have an opportunity to ask for his aid in the upcoming battle against Caelar Argent, and he will promise it without hesitation. If you do not ask for his help against Caelar and Schael Corwin is in the party, she will ask anyway and receive the same promise.
Afterward as long as you are not rude to Brother Deepvein, he will offer his services as a healer to the party.
====Siding with both====
It is possible to receive multiple rewards from this quest by pickpocketing the amulets in the dwarves' possession and giving them to Gurn in exchange for the Dread Hammer +2, then killing him and reporting his death for the remaining quest rewards. This is useful as he does not drop the hammer upon death.
More tactically speaking, your party will have a much easier time fighting the lich if they don't openly declare their intention to do so at the door.
==Rewards==
* The Secret Revealed for agreeing to stop Gurn Coldhearth
* Emerald, King's Tears, , and 40,000 total XP for destroying the lich Gurn Coldhearth
* Helmet of Dumathoin, scroll of Greater Restoration, and/or Brother Deepvein's assistance in the battle against Caelar Argent for reporting Gurn's death to Brother Deepvein
* Helmet of Dumathoin, Short Sword +1, Mace +1, Splint Mail +1, Medium Shield +1, 40 Bullet +2, miscellaneous nonmagical equipment, and 11,100 total XP for killing Brother Deepvein, Daran Highhammer, Semahl, and the three dwarven clerics
* Dread Hammer +2 and/or Gurn Coldhearth's assistance in the battle against Caelar Argent for giving Gurn the five amulets