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: When Andromeda and Perseus wake up on the beach, Andromeda tells Perseus that Argos needs a new leader/king. The problem with this is there is nothing onscreen to show that she even knew her father the King had died. She was hanging by her arms facing the Kraken and she couldn't turn around. By the time her father died, she was already falling into the sea, so again, she shouldn't even know her father has died.
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: Obviously, tooth fairies are real, in this movie at least. During the movie, Derek has to retrieve each child's tooth and put money under the pillow. He's paged as soon as the kid loses the tooth, since he often has to wait till the kid goes to bed before intervening, and he is required to do it as soon as possible. But parents are doing the same, and at one point in the movie Derek actually stops a dad that just did the swap and extorts the tooth from him. That of course creates a parodox: the majority of parents in the world apparently have been subjected for centuries to the freak occurrence of finding already under their pillows mysterious money and their children's baby teeth missing as they go do the deed themselves. You can't have both the fairy and the parent do the same task.
Suggested correction: This is part of the suspension of disbelief for holiday movies like this. Doing this means you would have to apply the exact same logic to every Christmas movie depicting Santa as real leaving presents for children when the parents would just see gifts appear they didn't leave behind.
I thought the same, but the thing is, it's all left to the imagination, for instance you can assume there's some "magic" that makes the parents forget everything and just assume they bought the gifts themselves even if they did not. If they meet Santa, it's considered a special deal, and its consequences are not shown, so it all stops here. Not here, here there are specific magic devices (a magic dust of forgetfulness exactly to erase memory of what happened, for instance) that in this encounter is not used by The Rock. So this movie is awfully specific about the interaction between the magical agents and whatnot, to the point that they need to erase their traces and not be spotted, but those rules don't make internal sense. Had they said nothing about it, I would have just assumed it was like every Santa movie as you mentioned, where it is not presented by the movie itself as an issue with contradictory solutions.