The Witch, The Return
You will get this mission only if you decide to kill the witch during your first meeting in [Witch Hunt] or change your mind and decide to kill her after talking with the priest in [Garadel's Scrolls].
The Witch is a very demanding enemy. She does use magic, but she's a healer, which makes her very resistant. It's best to fight her at close range.
You will unlock [The Return].
Once you deal with her, return to the village and tell the priest (M37:3) that you've dealt with the problem once and for all.
You will unlock [The Demon].
The Demon, Heart of the Demon
Depending on the path you've chosen, you can begin the mission in one of the two locations. The fight itself is the same in both cases.
If you've helped the priest
If you've decided to kill the witch in [Witch Hunt] or changed your mind and helped the priest in [Garadel's Scrolls], after returning to Garadel you will find all the villagers murdered (M37:3). You will learn the truth - the priest is really Aziraal's first-born, while the dead which has been protecting the village by weakening the demon.
If you've listened to Nalia
If you've listened to the witch in [Witch Hunt] and decided to follow her plot line and afterwards haven't changed your mind in [Garadel's Scrolls], you will meet Garadel once you get out of [The Catacombs] (M38:2). You will learn the whole truth about him being responsible for all the attacks and the witch protecting the village.
You will unlock [The Return Nalii].
He will transform into Garadel's true form - w powerful demon. He will be aided by a summoned pet. He will revive if you kill him, so focus on the demon. He's resistant to fire and deals massive damage. Keep on blocking all the time and use counter-attacks and specials. Make sure you have lots of healing potions and high fire resistance.
You will unlock [Heart of the Demon].
Once he falls, take the demon Garadel's black heart. Teleport to Alsorna and go talk with Cassara [Alsorna] (M1:7).
Before you move on, speak with Rogdor, Ghortarius and Dar Pha, who can be found underground [Alsorna - basement - Inside Alsorna] (M2:11). Once you decide you're ready, teleport to the Vahkmaar Castle's periphery [Vahkmaar Castle] (M39:1).
You will unlock [Whatever It Takes].
Nalia's Return & Aidan's Survival
You will get this mission only if you decide to listen to the witch during your first meeting in [Witch Hunt] and don't change your mind after talking with the priest in [Garadel's Scrolls].
After you kill the demon ([The Demon]), return to Nalia (M38:1) and check if she managed to cure Aidan. The woman will be young and beautiful again.
You will unlock [Aidan's Survival].
Aidan (M38:1) will be alive and will let you keep his amulet.