I was looking for more to read on Il Separatio. I found a document I believe was translated to Italian (from Latin). It was one of those mentioned in this article, like Codex Lugubrum. It was copy protected so I couldn't translate it.

Interesting that the entity was not considered the devil, but one of complete neutrality, yet almost more of an enemy to the church state.

By the way, it seems likely refuted that the Prague sculpture in the article represents Il Separatio.

The Hidden Origins of Il Separatio: Manuscripts Deemed Dangerous and Banned
[link to www.ancient-origins.net (secure)]

"Throughout history a large number of books have been banned only because they contained various uncomfortable truths or tales. Such books have been systematically hunted down and destroyed by representatives of the church or the state. Some copies have even been poisoned, thus giving the books a reputation of being cursed, as those who read them ended up dying due to the fatal poisons. Such was the case of books mentioning or telling tales about the entity known as Il Separatio."

"...Things got even more complicated as medieval texts discussed the powers of this entity. According to legend, the power of Il Separatio was 'absolutum' meaning 'absolute'. With such a description, it is not surprising that the medieval church banned all books mentioning Il Separatio and the Inquisition hunted down everyone who dared utter his name. Therefore, Il Separatio came to be known as Anonymus, 'The Anonymous One', 'The Nameless One', 'The One Who Should Not Be Named'."