Lucidstuck I

I know HOW they work, more or less at least.
I was asking if the process is more complicated for boss monsters. as far as I recall, uilos was not a boss monster.

Uillos is a boss monster. Emily's demonstrification skill works only on boss monsters, if it's used on any other monster the monster gets killed.(This is said kinda vaguely here but the wiki page makes clear that it pertains to boss monsters.) If he wasn't a boss monster, he wouldn't have survived the skill.

Since we don't have a soul increasing item from uillos, the skill doesn't automatically pacify a monster.