The Volunteer, Witcher 3: Wild Hunt Quest
1. Look around the area. / (Optional) Kill the troll.
Go to the place marked on the map, located near the White Eagle Fort signpost. There you will find a friendly rock troll, named Trollololo, who thinks that he is a member of the Redanian army.
He will tell you how he became a member of the army and also how by accident he killed several soldiers and then ate them because he did not want the food to be wasted.
If you decide that the troll (13) is dangerous ("Eating soldiers - makes you dangerous."), then you'll have to kill him.
It turned out the dubious musical talents belonged to a troll. Geralt felt the monster might be a danger to people living nearby, so he decided to end its life.
But if you think the troll had no bad intentions ("Got it. Wartime rules."), you will continue the conversation at the end of which troll will ask you to find some paint for him.
2. Find the paint the troll needs.
You can buy some paint from one of the merchants you can find in Oxenfurt.
3. Deliver the paint to the troll.
Take the paint to the troll. He will be very pleased and will ask you to paint an eagle for him, which is a symbol of the Redanian army. You may agree to do so, or convince him to try to paint it himself.
If you agree, you will paint an eagle that the troll will like very much, even though your work will look like a baby painting.
If the troll paints the eagle, he won't be satisfied, although his eagle will look much more "professional".
It turned out the dubious musical talents belonged to a troll who believed himself part of the Redanian army. His fondest dream was for fort he had been assigned to guard to look like a proper Redanian fort. Bear in mind that a troll's mental capacity is roughly that of a none-too-bright toddler, and you'll understand why this particular one felt a Redanian fort should be painted in bright Redanian colors. Geralt brought him red and white paint, which made him as happy as a child finding a present under his pillow.
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