Bloody Amber is a reward you get for killing Children Of Danu Order. This guide on What To Do With Bloody Amber In AC Valhalla Wrath of the Druids will tell you where to take the Bloody Amber and what you get for trading it in and killing all of the Children of Danu in the new DLC.
Most of the Children of Danu is optional side content that you can choose to complete or ignore. However, at least two of the members are part of the story so you will have to take a few of them out if you want to complete the Wrath of Druids DLC. After a few chapters of the main story you will meet Deirdre, a druid who helps make a potion to cure soldiers of a foul poison spread by the Children of Danu Order.
What To Do With Bloody Amber In AC Valhalla Wrath of the Druids
Once you meet her for the first time and complete the quest to get the cure for the Irish soldiers, she will inform you of the Children of the Danu. Much like the Order in Valhalla, you will need to find the clues and hunt each member down. Each one that you kill will give you a Bloody Amber. When you have all ten Bloody Ambers you return to Deirdre’s Hut to complete the Amber Sun quest.
Once you deliver them all, you will take a potion that let’s you fight Balor. If you can defeat him in battle, you get a new mythical spear called Gae Bolg.