On this page of the Assassin's Creed Valhalla Crossover Stories guide you will find a walkthrough for What Dreams May Come story quest. . During this mission, you and Kassandra will finally obtain the artifact.
If you have completed the Counting Sheep quest it is time to return to the cave which you visited earlier with Kassandra. Put the 5 shards in the right places - just one interaction, the character will do the action automatically. After completing this move, a huge gate will open.
Run forward all the time until you reach an area with enemies. You will pass through a platforming sequence and one area in which you need to swim. You will reach your destination without any problems, there is no possibility to get lost.
When you see the opponents, take care of them. Kassandra will appear to help you get rid of them. If you won't take care of enemies, you won't proceed further.
Setting the rays
After eliminating all enemies, time for a short puzzle. You need to position the rays properly. Start with the one to the left of the door. Direct the ray to the point below.
Jump down and position the light so that the beam reaches the object right at the gate. With that, the first part is done.
Return to the main area of the room. There is another reflective object at the entrance to the room. You must move it back and to the left, this way the ray will reach the next object.
The last thing you need to do is direct the beam so that it reaches the door. This will open the gate and you will be able to save the island and complete the mission.
To complete this quest you must reach the artifact. Its power will be too strong for you, but with Kassandra's help, you will handle it. A short conversation will conclude this mission.