Good questions, although I'd expect no less from you.
(BTW, I'm still a bit off center from this food poisoning. Not a fun deal, I can tell you that!)
The Gleanons and the Mites were my own creation. One of the great things about working with Mattel and Mark Taylor -- then at Jetlag, now running Nickelodeon Animation Studio in Burbank -- was that they gave me so much creative latitude in so many areas. And one of the places they really did this was in allowing me to create sub-characters even though those characters would never appear as action figures in the toy-line. Of course you always have to be careful about dancing in new characters because it takes away time from your main cast. But to do it once in a while is fun and I think Mark and Mattel got a grin from it.
I LOVED the Gleanons and the Mites.
As for your question about Skeletor aligning himself with the Mutants or Crita, that's a tough one. For sheer firepower and numbers, he'd have to lean toward the mutants. But for brains, wile and...hmmmm...he'd ben inclined toward Crita. (I know I would.

) Also, remember that, in my proposal for Season Two, I had a triumverate of females in charge of Eternia, so I think Skeletor would wisely want Crita's female input. If I know Skelly, I think he'd try to work the best of both worlds, using the mutants as his henchmen and Crita as his second-in-command, at the same time playing one faction off against the other so neither gets too comfortable. However, if I was in his place and I had to make a definite choice of one over the other, I'd have to go for Crita. But then I've always been drawn to powerful, intelligent, confident women -- all of which adds up to 'hot' in my book, Lucy Lui and my Irish wife being prime examples. I do believe that this is something Skeletor and I have in common, so there you have it.