I never really considered how much of an extra mile of evil Demona went there. She literally went around town, picking random people off the street with a mace for fun.
There's a reason Demona is my favorite Disney villain after Maleficent. At the very least, she's the House of Mouse's most complex antagonist and a gift to Western animation.
Her confrontation with the Weird Sisters remains a favorite scene of mine. They're essentially right when they throw her questions right back in her face. The massacre at Castle Wyvern -- and by extension, the entire series -- is all Demona's fault. And she can't accept it because she's too consumed by guilt, blaming the humans instead. Goliath's disgust at her ignored epiphany is poignant and really underscores the tragedy of Demona.
Yeah the whole thing that makes Demona such a great antagonist is that she has meaningfull reasons for why she's the way she is and in case you're wondering what I mean by meaningfull, I mean that those reasons aren't there just to give her a tragic backstory but rather they affect her actions in the present for good or worse.
All too often a villian is given a "tragic backstory" but it really doesn't change anything about the villian, you don't really view the villian's actions in any different light then before and that backstory doesn't seem to have any effect on the present.
Pretty much all the antagonists in gargoyles (at least the first 2 seasons) had some desent reasons from a story PoV as to why they act the way they do, those reasons might be stupid from an in universe PoV but at least they seemed like those reasons truly mattered.