Although skekVar the General did not appear in the original The Dark Crystal (1982), the character had previously appeared in Tokyopop Manga series "Legends of the Dark Crystal" (published 2007-2010) as well as in the graphic novel "The Dark Crystal: Creation Myths" Volume III (published 2015), at which time he was known as "The Ambassador."
When Rian comments on Mira having wings, Mira responds saying "Of course I do. I'm a girl." This is most likely a parallel to The Dark Crystal (1982). When Jen tells Kira that he doesn't have wings, Kira responds saying "Of course you don't, you're a boy."
The creatures that the Skeksis use as wheels on their carriage are called Armaligs. According to J.M. Lee's reference book that accompanies the series, "Heroes of the Resistance," Armaligs primarily lived underground, making their burrows and colonies in the root networks of the trees within the Endless Forest. However, by the time of this story, most Armaligs are extinct, with the remaining few living in captivity within the stables of the Castle of the Crystal.
The furry green creature that appears to live in the Vapran library is a Pluff'M. According to "Heroes of the Resistance," it is the elder librarian's personal familiar.
The Sanctuary Tree is called "Vliste-Staba" in the Gelfling language. It grows on the mountains near the Grottan Sanctuary. Its roots are made of glittering stone and penetrate deep into the mountains.