A Sackful Of Fluff is a Witcher 2 Assassins of Kings Enhanced Edition quest available during the second chapter of the game.
A Sackful Of Fluff quest requires your presence in the Old Quarry, south of Vergen, thats why you should complete it while playing the main quest known as Hunting Magic.
“I suppose you must be wondering if, while keenly pursuing the kingslayers, Geralt took on any errands of the kind he was wont to complete. I have in mind such pursuits as the extermination of monster colonies and the collection of rewards for impressive trophies cut from the corpses of slain beasts.
I delved into my memory and search for something that might answer this question and, recalled and adventure in this very vein. Our hero was retained by an individual named Elthon, who lived in a hut by the quarry near Vergen.
Elthon was willing to pay good coin for harpy feathers, which he was purportedly amassing for a certain collector. In exchange for a pouch of orens, Geralt was to bring Elthon twelve impressive plumes.”
When to start
As soon as you activate it, while playing Hunting Magic
To activate A Sackful Of Fluff, you have to find Elthon, therefore when you reach the top of the quarry, look around for a cottage. It should be to the right while facing the quarry.
Elthon, as the description says, needs Harpy feathers, but you should know that he needs more than 12. In fact, this quest has several phases. For the first phase, Elthon needs 12 feathers, and then he asks for 60. If you manage to gather all of them, he will need 8 more.
Because the amount he needs is high, make sure that when you start to descend in the quarry you kill and loot all harpies you encounter, including those within the tunnels you have to explore to finish Hunting Magic.
After you complete Hunting Magic and The Harpy Queen Contract; on your way to Vergen, visit Elthon, and give him the feathers.
Note: Every time he asks for more, you should accept, or you will fail the quest.
For the final phase, you will be asked to visit Elthon later. Exit the hut and meditate for a short time in the forest nearby.
Now, return and see the strange character dresses as a chicken. Talk to him but dont be rude. Offer him another feather if you have and then ask him about the weather. Leave his hut with Elthons Trophy and another quest completed added to your journal.
Note: If you cant find enough feathers, meditate and the Harpies will respawn.