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.
Family-Unfriendly Aesop: In book 2 of ''Beyond The Spiderwick Chronicles, Laurie explains that she lies because "lying works," and nothing in the story contradicts this claim. This, from a book aimed at 6-12 year olds.
Mulgarath and his unnatural eyes is an incredibly nasty customer in just about any of his forms, though his native (ogre) form wins the prize for sheer ugly. The goblins and trolls aren't exactly going to win any beauty contests, either.
"Click klack; watch your back"
The Banshee from the field guide.
The field guide terrified this troper as a child, especially the troll descriptions. The book is probably what gave me my fear of The Fair Folk.
Anytime a character has to face goblins or other unfriendly without the stone or hobgoblin spit to let them see them
The fairies drowning in honey in the last book. Jared saves a few but is traumatized by the experience.