Finally finished this Xornoth peice that's been in my back log forever - not enough fun designs for their demon form so here's take and some head cannons under the line
I like the idea he was the favorite kid who was expected to be the champion of Aeor when they and Scott were kids. Like Xornoth was the golden child, except he wasn't. He was trouble maker, charming and loved by all of rivendell but because every mistake he made was hidden and they got away with it due to being the expected champion; I like to think they got the fire powers from Exor but was born with nether plant magic, which would seem much more beneficial and charming in rivendell where there's already snow all the time making Scott's powers useless and seem like a bad sign.
I like to imagine this made Xornoth delusional as he got older, thinking they actually were meant to lead rivendell and be the champion of Aeor, but Scott stole his fate. That Xornoth thinks he's still the good one and this is all Scott's fault for ruining their fates. I feel like it's a fun motivation for them to despise Scott more and more. Also imagine he started to follow Exor out of curiosity, thinking he was so above it all that it wouldn't matter if he dabbled in it. Ie: Xornoth's Ego is their downfall while Scott's self loathing is his.