Xanathos, though a good guy, could still be, maybe at times, a bit ruthless in certain business dealings and he'd still be someone you'd want on your side. Not every good guy is a boy scout afterall.
Demona has an entry on the gargwiki, though it has a lot of spoilers and I've not read a lot of it since I've not yet seen all of season 2.
http://gargoyles.dracandros.com/DemonaFrom what I remember when I use to go to Greg's website he wouldn't reveal certain things but he did say some stuff like she and macbeth were magically linked by the weird sisters so they don't age and can't die till one slays the other. Also her changing into human form at daytime is painful, and was a gift from Puck. If you've seen certain episodes of late season 2 you know about who Puck is. And he also said that she would be eventually redeemed. I guess it would be during the alien invasion of 2198. Where Brooklyn did appear during his travels in time. Greg said he made 2 extended stays there. Though some of this version of his timeline is altered with Jason and his friend's interference. But that is and what happened to the phoenix gate to free Brooklyn and his family from it is another topic.
Greg also said that her desire is she still wishes to protect her clan and all gargoyle kind, but that it has become very twisted.
Also Sara doesn't need to speak or move to cast her spells. Unlike the natives to the gargoyle universe which greg says they have to speak their spells. Though the latin thing seems pretty stupid. Why no spells in ancient egyptian, babylonian, sumarian, and other older languages. Or for the new world, toltec, myan or aztec. So all of gnash's spells well be in modern english. It makes what Greg said that Oberon and other ancient folks of his race were just sitting around twiddling their thumbs waiting till Latin was invented before they could cast any spells when ancient Egyptian, Sumerian, Babylonian and such were being spoken by humans. and I"m not good at ryming so his cantrip spells may sound like, "it's to dark in here I need some light." "This drink is to hot I want it cooler." and such like that.