Part 5: Trolls 3May as well try for crop yields and hope for the best.
Thanks again to Mors Rattus for another great background post. I'll try to chime in (as here) with some augmentation and differing perspective. I think it's fairly clear the latest write-up is from the Uz point of view.
Wonderhome is what the surface people think of as the Underworld. So when Orlanth slew Yelm with Death, he sent Yelm there. That, in turn, drove the trolls onto the surface, which was conveniently darkish (since Yelm was dead and in the Underworld) but also full of rampaging Chaos things. While the trolls were and are resolute foes of Chaos, their appearance on the surface was still seen as a mixed blessing. In part, that's because their attitude towards anything not Uz is that it's food.
With the right ritual, a troll can honor a non-troll by eating him. Since the Uz don't think of trollkin as real Uz, that means that a particularly valued trollkin might "earn" his way into a priestess' stomach in the hopes of being reborn as a dark troll. Uz will eat less valued trollkin in times of need, of course. Valued trollkin are sometimes treated a little better than the rest, so it's really a fine line between being treated with a little respect and being a meal. (Being an enlo sucks, basically.)
There are hints in some of the tales that when Kyger Lytor confronted Nysalor, she brought something Pre-Dark along to deploy as a weapon. My sense is that Nysalor turned it against her and that the Trollkin curse is the result. That would also explain why all the Uz heroquests seeking to reverse the curse failed, as trying to fight Nysalor simply strengthens the whammy. (No sensible priestess would deliberately try to fail such a quest given that any catastrophe resulting could well be worse than the current curse.)
What's Pre-Dark? That's ambiguous, but there are some strong hints that something existed prior to the Celestial Court. Some Pre-Dark demons died and then became parts of the world. Some were torn apart and the pieces became parts of the world. Some could do neither. A few may have become members of the Celestial Court or may be present in other guises in the "modern" Glorantha. The Orlanthi name some of them things like "Too Big to Think of," "Can't Be Moved" and "Before Still." (Pre-Dark and Chaos may or may not be the same thing. It's entirely possible that prior to Creation, Chaos existed not as inchoate nothingness but as an alternate paradigm of existence which the Celestial Court overthrew, adapted or destroyed to form Glorantha.)
Personally, I've picked up on little hints that suggest that Zorak Zoran may in fact have started out as a Pre-Dark demon who converted to the new ways. As God of Hatred and Rage, he certainly fits the model.