Az'zoxish is the parent of the Lords in Black
In a livestream with Jim Povolo, Matt Lang stated that the Lords in Black (and presumably Webby and the other Queens in White) are the children of an ancient chaos entity.
The Lords in Black are worshiped by a cult known as the Church of the Starry Children. This phrasing implies that the "Starry Children" are the beings being worshiped, not the members of the cult, drawing further attention to the Lords in Black's parentage.
In Workin' Boys, Cassandra King's program bio states that "Pain is the language that unites the children of Az'zoxish no matter which star they may hail from." We know the Lords in Black want to conquer the whole universe, not just Earth, because in TGWDLM the hive (through Alice, Deb, and The Hatchetfield Bee) says "We have traveled across seas of stars bending countless civilizations to our will," and in The Witch in The Web, Willabella claims that "All worlds are theirs." Plus, pain absolutely is the language of the Lords in Black, as they, through their disparate goals, all seem to take delight in causing it.
Cassie's bio starts out by referencing her inability to deny the reality of prophecy, and painful visions she receives. This is consistent with the way the Lords in Black send visions of the future to those with a touch of The Gift in order to manipulate them.
The second half of Cassie's bio is more confusing, but doesn't rule out this possibility. She seems to be describing a vision she's received which she can't quite make sense of: "Cassie wants to see what lies at the end of the cold half. She's ready to see the face of the girl screaming in the dark. How did she find herself aboard? And what is the destination of such a significant ship?" The "cold half" could just be referring to the nature of the pain this part of this presumably recurring vision causes her. The girl screaming in the dark could be Hannah, but there's not much evidence. Maybe it's Cassie herself, since she believes she is going to "depart" soon. The ship is interesting to me because Pokey's meteor seems to function as a spaceship, considering its ability to land precisely in a dense crowd of people gathered at a Black Altar in TGWDLM. Perhaps Az'zoxish or another Lord has some sort of ship too? Or maybe it belongs to CCRP? We know they have a mining colony on the moon and were likely also behind the mission to harvest samples from the meteor to create Otho.
Regardless of whose ship it is, it appears in a powerful recurring vision, which leads me to believe that Cassandra King has at least a touch of The Gift and is a disciple of Az'zoxish, similarly to Hannah's relationship to Webby or Willabella's relationship to Wiggly. The similarites in these relationships lend greater evidence to the idea that Az'zoxish is a similar being to the Lords in Black, presumably their parent. Given her relationship to the Starlight Theater, it's likely that Cassie is a member of the Hatchetfield Community Players, and therefore will appear in Cast Party Massacre.
Consider this structurally too. The Langs seem to be setting up Orbweaver as a climactic moment for the series, with Nick Lang stating a while ago that when McNamara next returns the overall story will be nearing its end. However, it's unlikely they'll film and release Cast Party Massacre before Orbweaver. Though I'm sure it will be written to be enjoyable and comprehensible as a standalone piece, they won't want it to seem anticlimactic to the fans who've watched all of Nightmare Time. Nerdy Prudes Must Die is a good example of this, where it introduces the Lords in Black to the characters (and therefore the audience) as a new concept, but heightens the overall story by having them act as a group for the first time in the series. Centering Cast Party Massacre around the parent of the Lords in Black would accomplish this perfectly.
Thanks to @abiimaryy for transcribing the Workin' Boys program bios!