Originally, dracocheesecake and I made that AU just to have an excuse to have SkekGra and UrGoh have GraGoh as their hybrid baby and it was called UrSkek babies AU. Then we were like "holy shit we can actually go further that AU with UrRu and Skeksis as natives of Thra has lots of potential !" and the Natives AU was born. However we never forgot the UrSkeks situation
In that AU, UrRu and Skeksis hate each other but they are biologically very similar, being "cousin species". So reproduction is not impossible. The babies born from those unions are UrSkeks. They look exactly like my redesigns in the normal continuity (humanoid primate-feline faces, much taller, also levitate and have telekinesis, etc). But they are forbidden. The races are enemies so a romance or WORSE reproducing together is seen as the biggest sin on both sides. UrRu and Skeksis lovers banished, never without ritualistic torture on Skeksis side, if they are not imprisonned or killed by the Skeksis too. But UrSkeks are rarely born from romance anyway given how hateful the species are, they more often are the result from rape, hatefuck or drugs/alcohol nights. The baby is rarely loved by the mother, being immediatly seen as a sinful abomination. So if they are not killed, either they grow in an abusive household without any love, or were sold the earliest possible as a slave where they are treated like strong animals for the hardest tasks. Skeksis and UrRu see them as ugly so they are very rarely used as sex slaves, just like workanimals traded across all species even Gelflings, ignoring or even not knowing the fact they have a mind on their own since they are seen as not real people. Lot of UrSkeks grow depressed, bitter, cynical and many become as bad as their owners ready to vow revenge whenever they will be able to and be free. But they are chained with electrical Skeksis chains that electrify them whenever they try using their powers.
UrSkeks are not very numerous since the occasion to make them are few and sincr half of them are killed at birth, but some very very lucky ones had loving parents and either lived free all their life far from society or sadly were captured later by others. That's like the one I drew here who is this AU's version of Lore. Instead of being a rock gollem, here he is the mute youngest son of SkekGra and UrGoh. He sadly got captured by Dousans when he was around 8 humans years old and remained a slave for 240 trines, holding on hope tight while his family thought he was dead... until he would meet Brea. Meanwhile their older son, GraGoh, remained free all his life and even was the "co-creator" with his UrRu mate of a new species : the Rusis, mix of UrSkek and either UrRu or Skeksis, looking like a perfect mix of both more than UrSkeks do with feathery wings, in short lil dragons inspired by meladromatic's UrSkeks redesigns

The Dark Crystal, UrSkeks and Lore © the Jim Henson Company
AU, ideas, theories and how Lore is an UrSkek and son of SkekGra and UrGoh in that AU © dracocheesecake and me
Drawing, UrSkek redesigns and Lore's UrSkek design © me