This can be done on casual. Collect as many points as possible and get to the sentinel artifact. Once this is done there are 3 possible stone locations, the master bedroom, library, and wine cellar. Go to the master bedroom first because it wont cost you anything to get over to it. Kill zombies by the stone until you fill it up and then gaze into it. You are looking for a clock. If you get the clock right away that’s perfect but in the video I fill up all 3 to show all possible locations. You will also notice I knife multiple vases in the 3 stone areas because the stones will rotate within each area. The Wine Cellar has 2, Library has 2 as well as 1 i miss above the Library in the study, and the Master Bedroom area has 3. (Master, Trophy, Bedroom Hallway) Once you get the stone that shows the clock you will have to match it up. The stone will show 1 of 3 clocks and you need to go to the correct one. When you have enough I would advice buying a machine gun off the wall before you start the clock. The locations of the clocks are shown at 05:10 starting with main hall, billiards room, and the dining room. Once you find the correct clock hold X in front of it and defeat all the zombies while not leaving the circle.