Visible crew/equipment: Thin wires are visible, attached to the crystal bats as they fly off to watch Jen and Kira.
Visible crew/equipment: When the evil birds send the big beetle-like monsters out to look for Jen, they run into a tunnel. When the beetles run to the camera you can see that between their legs, there is a pair of human legs.
Visible crew/equipment: During the landstrider sequence, before they reach the Crystal castle, you can just make out in one shot, the safety wire attached to the performer as he runs. (DVD extras says the landstrider performers had these wires all the time but this is the only time you see them).
Visible crew/equipment: Shortly after the scene in which Jen sees someone shatter the Dark Crystal in a vision from the Crystal Shard, there is a panning shot following Jen through the forest during which you can see the shadow of the camera in the foreground.
Answer: The skeksis and the beings of light are the same, each being a different side (good and bad) therefore it was there evil side (the skeksis) that struck the crystal.