Well, i ave not really ever sat down and thought about The Dark Crystal thematically.. At first blush, I would not say that it is esposing a pantheist approach at all. I'll give it a go though - what happens in the story, and what does that mean?
To summarize - before the action of the film begins, their exists a race of very intelligent beings on the planet who use a large crystal to harness the power of the sun, and accomplish various things with it. They come up with an idea to use the power of the crystal during the great conjunction in order to anhialate all the evil or impure parts of their character, rendering them perfected beings, and immortal. (It is unclear, but there is some reason to think they hope to become wholly spiritual beings in this process.)
Their attempt fails, the crystal cracks and a shard is lost. Instead of purifying them, they are split into two separate, physical, races. The Skeksis are highly intelligent, cruel, clever, technologically advanced and creative, and have a strong will to power. They only respect strength. They wish to remain as they are and dominate the planet, becoming immortal one the next great conjunction comes.
The mystics are wise, kind, and intuitive. They seem to be closer to nature and live simply. They are not terribly active, seeming almost passive at times, though they do persue plans to reunite themselves with the Skeksis and heal the crystal and the planet. They use a sort of magic that seems focused on patterns and doing things at the right time.
After the split, the Skeksis drive out the Mystics, ruleing the planet with an iron fist. They in particular dominate the simple Pod people, using them as slaves and to drain their life essence to maintain the youth of the Skeksis. There is a prophesy however which says that a Gelfling - a humanlike race - will heal the crystal and the split between the two groups. The Skeksis round up and slaughter all the Gelflings to prevent this.
The Mystics, however, have saved one Gelfling, a baby named Jen, and raised him. At the begging of the film, the leader of the Mystics sens him on a mission to find the crystal shard and heal the crystal. He tells him to go to Aughra for direction.
Jen finds Augrah, who seems to be some sort of scientist, and finds the shard. She tells him that the task of healing the crystal must be completed before the Great Conjunction, or all is lost. The army of the Skeksis, beetle-like creatures, attack, and Jen flees. Augrah fights them to give him time to escape, and is captured.
Jen leaves, and on his journey meets with a Gelfling girl, Kira, who was raised by Pod people. While they are together, the Skeksis army attacks the settlement, and the Gelflings flee. They find an old ruin of the Gelfling people, which is quite extensive, and contains murals depicting the events of the splitting of the crystal and the prophesy. Jen realizes what he needs to do.
They are set upon though by one of the Skeksis, who had been cast out of the group. He captures Kira and brings her back to the castle, where they decide to drain her essence. She escapes in the castle before this happens.
As the Conjunction approaches, Jen meets Kira in the crystal chamber. The Skeksis gather there, and the Mystics also appear having traveled for many days. In an attempt to place the shard back into the crystal, Kira is killed by one of the Skeksis. Jen places the shard in the crytal, and the Mysics and Skeksis are reunited into single beings. The beings revive Kira, seem to turn things over to the Gelflings, and leave (to where is not clear).
So what is going on here? A lot obviously, but i just have a few immediate thoug.
What were the original beings trying to do, and why did it fail? I think it would be wrong to associate the Skeksis simply with evil, and the Mysics with good, though clearly the attempt on the part of the original beings was to get rid of the "bad" elements. And the Skeksis clearly lack many things, notably kindness and wisdom. But they are very clever, and they get things done. The Mystics, on the other hand, can seem almost impotent, incurious and passive. They use their magic to see what nature, the logos says to them, but they are not creative, they do not make things happen.
I don't really see this as a Yin Yang thing myself. More a matter of each aspect or function of our being having a dark side. The original beings had taken a sort of dualist approach, and we trying to shed matter and make themselves pure and good. What they found was that they were, in fact, integrated beings, and taking away the "bad" meant losing some of the good too - the things that were evil were in a way perversions of good things. They were truly incomplete.
The result of the split affects the whole planet - it isn't confined to the originators. And it is the Gelflings that are supposed to be the ones to heal the split - the Skeksis don't want to and for whatever reason, the Mystics can't. The Gelflings in some ways seem the most like the Beings themselves - with the potential for intelligence, wisdom, and action. It's hard to imagine the Pod people undertaking the quest, or even Auhura, though she is brave and good. She seems to have a kind of external relationship to the whole thing.
