Ancestral Light is a hidden ability in Ori and the Will of the Wisps, so you can play through the entire game but never receive it. Ancestral Light is a unique ability, because there are actually two trees that give it to Ori. Ancestral Light makes Ori’s attacks do 25% more damage. If you get both Ancestral Lights, then Ori will do 50% more damage. That is a huge bump in damage, and can make defeating enemies a whole lot easier. So where can you find these hidden spirit trees?
You can access the first tree from Silent Woods, as a reward for completing a quest. To pick up the quest you must teleport to the first Spirit Well in Silent Woods. Then go to the left and you will encounter an NPC. Talk to him and he will tell you how the trees he once cared for have died. He then asks you to find help to see if the last tree in his care can be saved, and gives you a tree branch.
You must take this tree branch back to Wellspring Glades and talk to Tuley. He is the gardener for Wellspring Glades and is the one that helps you improve the glades by planting seeds you find. He will tell you the tree cannot be saved.
Ori is basically just a messenger in this questline, but for a great reward. After hearing this news, go back to the NPC in Silent Woods and he will give you a seed. Take this seed immediately back to Tuley, who will plant it for you. Magically, the tree grows instantly, and all you must do now is absorb its light. This gets you the first 25% damage bonus.
The next tree is located at the very bottom of Inkwater Marsh. In the image below, I have included a map of Inkwater Marsh and circled the area you need to be in. You only need the Bash ability to get to this one. Once you get to the area with three blue flowers, you are in the right place. What you have to do next is hit these flowers in the correct order to open up a hidden door. Behind that door is where you get Ancestral Light.
Here is the order you must hit the flowers in: left, middle, left, right, right, middle, left. When you hit the last flower, you will hear a chime and the door will open. Go through it and you can now absorb the spirit tree’s light. Now you have the full 50% extra damage on Ori’s attacks!
Ancestral Light will remain active for the rest of the game. You do not need to equip it and you cannot see it, but it is there. Ancestral Light will also be active in timed boss trials, so you can use it to speed up those boss fights even more!
I hope this guide has helped you out, and enjoy your new power! Below I have a video showing everything I have talked about if you need additional help.