I love League demonology so this isn't necessarily a criticism, but does Ashlesh the "Demon of joy" even make sense as a concept?
Demons represent things that haunt people.
Fear, addiction, agony, secrets, nightmares. These are things that plague peoples thoughts.
Joy is inherently a fleeting feeling with no real downsides.
There are negative variations of happiness but these are usually described as mania or limerence. A lot of these start to fall more into the category of love etc.
Maybe it's me who's missing something, but what does Ashlesh actually represent? Is he actually evil? Does he torment people? Or does he just feed off positive emotions which technically makes him a demon?