Plot hole: In the second Shrek movie, we find out that Fairy Godmother and the King had a deal that Prince Charming would save Princess Fiona from the keep, hence becoming her true love and breaking the curse. In the fourth movie, we start with Rumple monologuing about how he almost had the Kingdom by signing a deal with the King. Why would the King be so desperate to try and reverse the curse by signing a deal when he knows he has a prior attempt through Prince Charming, assuming it would take the same time for the messenger to return with news about Charming and Fiona either way?
Suggested correction: It is stated in the intro that when "days turned into years" of waiting for a Prince to rescue Princess Fiona, the king and queen resorted to more desperate measures - enter Rumpelstiltskin.
Plot hole: When Astrid gets on Toothless for the first time, Toothless takes off uncontrollably and tries to scare her. Hiccup seems to have no control over him at this time. How is that so if with the new tail fin, Toothless cannot fly without Hiccup's precise control of the tail fin? That whole sequence would have fallen apart. This mistake was even admitted to on the DVD commentary. (00:53:35)
Plot hole: In Aunty Em's Emporium, when Medusa turns the older woman to stone, she has hold of Annabeth's wrist and Annabeth cannot free herself. Grover comes along later, as Percy is keeping Medusa busy, and breaks the arm of the statue that is holding Annabeth (near the elbow). Annabeth is able to easily pry the statue's severed arm's grip from her wrist, even though the fingers and thumb weren't broken at all, meaning she could have easily freed herself at any time.
Plot hole: The movie is based in 1986 after the group time travels from 2010. That makes it a 24 year trip back in time. It is stated that Jacob is 20 years old. That is an error as this would make him roughly around 23 or 24 if he was conceived in 1986, which we saw near the end of the movie.
Suggested correction: This mistake has already been corrected. Cusack could have simply generalized his age when he mentioned it, probably not remembering his real age at the moment.
Plot hole: How does Horatio (a Lilliputian) get to Glumdaclitch's dollhouse, which is on the second floor of the house? Jack Black is twelve time smaller than the Brobdingnagian, and the Lilliputians are twelve times smaller than him. How did he get up the stairs? Getting to the second story of the dollhouse would be challenging enough.
Plot hole: In one of the last scenes when the scribe is putting the newly published bible on the shelf you can see next to it a big green book with the word Tanach written on it. That is actually a translated bible with the Hebrew and English, including the five books of Moses and psalms plus much more. He had the Bible the whole time. (01:47:50)
Suggested correction: From the internet movie database... The Hebrew Bible, or The Bible or "the Chumash" in Hebrew, is already in the library. The Christian "Old Testament" is the Chumash with some variations (reorder of books and reorder of the 10 commandments, depending on religious denomination). The New King James Version is an Old Testament with the Christian Gospels added at the end, some of which the main character, Eli, quotes. These two books would be considered separate and unique in a library.