These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Was Matilda truly a demon, or was it a lie by Lucifer to torment Ambrosio?
Complete Monster: Ambrosio, the eponymous character, is an epitome of a Sinister Minister character type and the story is about him falling from grace after being tempted to sin. The first scene showing him preaching to the audience hints at his prideful nature. After breaking his vow of chastity Ambrosio jumps to committing kidnapping, Black Magic, rape, murder and incest before selling his own soul to Satan, the only supernatural element left unambiguous in the whole story.
Fridge Horror: The conspiracy of nuns who knew Agnes was still alive were all killed by the angry mob. If Lorenzo hadn't come across the secret of the statue, she might have never been found.
Older Than They Think: The scenes between Raymond and the Bleeding Nun are interestingly similar to Jonathan Harker's encounter several decades later with the three brides of Count Dracula...
Agnes' narrative style when she tells the story of the Bleeding Nun also bears a striking resemblance to Henry Tilney's in his famous monologue parodying Gothic literature in Jane Austen's Northanger Abbey, which also references The Monk at a different point.