Way to unlock the quest: Talk to Vivienne after you complete the Wicked Eyes and Wicked Hearts quest, as well as the quests for the enchantress before that.
Quest giver: Vivienne (M12,1)
In Skyhold, after you complete the Wicked Eyes and Wicked Hearts main quest, talk to Vivienne (M12,1). She will offer you finding the heart of a snowy wyvern, which she needs as an ingredient for her medicine. If you refuse her offer, you will lose the chance to complete the quest later on.
If you agree, on your map of the Exalted Plains, there appears a marking for the approximate area, where you can find the wyvern. It inhabits the areas of the marshes. It is easy to tell, by its white color. Kill the beast (level 15) and loot the corpse - you will pick up the wyvern heart. Return to Vivienne for your reward.
Rewards for completing the quest:
- Experience (lots)
- 400 Influence points
- 3 Power points