You'll reach a new chamber containing a shining sphere. Pick it up and place it on the pedestal, then climb on the golden brick to cast a shadow on the wall. This will unlock the way forward - continue following the fox. The new room contains a bipedal robot - use the shining sphere to jumpstart him. Follow him - the robot will clear the roots, but the action will disable it. Fortunately, it will send you a vision regarding the future events.
Use the unlocked passage and cross the bridge to reach a very dark cave with harassing shadows. During this stage of your journey, the shadows will engage you and attempt to drain your health. Avoid the shadows and try to keep a safe distance. In this case, run straight ahead, avoid the opponents, and keep running until you've reached a shining sphere. Use it on the shadows obstructing the way forward to leave the current chamber.
You've entered the next part of the cave. Use the wall on your left to climb to the upper level and land on the right side of the shadow. Lure it from its initial location in order to reach the shining item. Use the sphere to dispose of the lured shadow and those in the near vicinity, and then use the ledge to climb to the upper level.
Turn left and follow the ledges to reach the next floor. Bypass the shadow and proceed forward to get past the large stone. Use the stairs and grab onto the nearby ledge to climb higher. Now, descend the stairs and proceed down the river. Go straight ahead and enter the bridge on your left.
Follow the stairs - you should encounter your companion. Follow him and get past a very narrow door. Climb to the ledge on your right and follow the ledges to reach a chamber with a smashed door.