QWe do not use the sellie vs unsellie stuff much, really, but that is a "IMS" issue. The worst bast5ard we have faced (among the fae) was a "sellie" (summer, light) faerie that rejoiced in massive displays of colourfool fireworks. You get it: flaming knight of doom akin to a rider of the apocalypse. "Sellie" fae tend to be haugty and unpredictable. Unsellie haughty and distant. Both rejouice in causing mischief, not by mischief itself, buit because they do enjoy watching the humans do "weird" (read: logical and/or innovative) stuff to solve the problems.
It is lñike going to the cinema for them, really. Unsellie fae prefer dramas and ddark terror movies. Sellie fae prefer action movies, comedies and hecatombe world of doom movies.
Roughly speaking, but the division in good/bad does not apply very well to our sagas' faeries.
Cheers,
Xavi