Puss and Donkey switching bodies seems random. But the two held hands when they were transported by Merlin's spell. That's why only they switched.
It may seem odd that Little Red Riding Hood has a cameo as a villain in Shrek 3, but then remember that her enemy the Big Bad Wolf is one of the good guys.
Or she might be getting revenge on Shrek and Fiona... because they scared her off during their honeymoon in the second film. If so, that's Disproportionate Retribution right there.
We meet Fiona's four princess friends: Snow White, Cinderella, Sleeping Beauty, and Rapunzel, the last of whom is a turncoat who sells them out to Prince Charming. There's some foreshadowing there, with Rapunzel's bickering with the others being far less good-natured than most of their friendly ribbing, implying Rapunzel is The Friend Nobody Likes. There's probably a good reason for that, one that neither the film nor Word of God would ever be allowed to say out loud: the reason the other princesses pick on Rapunzel, and the reason for her bitterness that leads to her Face–Heel Turn, is probably that she's the only one of the foursome who doesn't have a Disney film. Disney wouldn't make a Rapunzel film until three years later, while the first three had been Disney characters for over half a century. In some weird fourth-wall-breaking way, Rapunzel is probably somehow aware that she's not at all on equal footing with the other three.
Isn't it convenient the only Disney princess (Ariel) who canonically has a kid (Melody) is on bad terms with Fiona? This is backed up by the fact The Little Mermaid 2 was made in 2000 predating all the previous three movies, so (assuming DreamWorks kept up with the competition), they had to have known about it.
King Harold's Sudden Sequel Death Syndrome makes sense when you consider the average lifespan of a frog is only around 10-12 years. After living a reasonably long life as a human, he's become far older than any frog should be and so his years simply caught up to him.
Artie's speech in the end really does get through to most, if not all, of the villains because the person they are trying to kill, Shrek, has already proven that you don't have to stay as the Villain everyone thinks you must be. Hell, last movie had the typical Fairy Godmother be the main villain, this film ends with the villains getting the same opportunity as Shrek, live out the lives that makes them happy.
Arthur Pendragon only became king in the original mythos because he pulled the holy sword Excalibur from the stone. However, in this universe, there's no sword to pull, because Puss in Boots: The Last Wish reveals that Jack Horner has it.
Charming completely failing to kill Shrek in the climax by missing his sword stab and it instead landing underneath his armpit without harm becomes even more hilarious when you realise that shoving a prop sword/knife under the armpit not facing the audience is a popular location for actors during fight scenes, especially since we've seen him greviously wound other actors playing the role of Shrek, only then landing a safe hit on the ogre himself at the worst possible time.
Some may not understand why Artie was so unpopular and bullied in school despite the fact he is a nice guy. But his father is Uther Pendragon and if he was like in the tale it's possible that the other students are bullying Artie because of what he has done.
In the Bad Guy Bar seen near the beginning among the specials advertised by the sign hanging from the ceiling is "Crunchy Children Fingers". Think about that one for a second.
Unless it's a take on "Lady Fingers" or some such.
Shrek tells Artie that when he was a baby, his father tried to eat him. No wonder he wants to be left alone in the first film, as if this statement is anything to go by, he had an abusive childhood so it seemed like the whole world hated him, including his parents. Poor guy...
It also explains why he was so afraid of becoming a father himself. He though of his own abusive father and was worried he'd repeat the cycle and have the same relationship with his future children.
On that note, remember when King Harold accused Shrek of potentially doing the same in the previous installment, during their dinner argument? He may well have struck a sore nerve there.
It is pretty frightening just how close Charming was to a complete victory. He already had staged a successful coup d'état and was in control of the kingdom for a day or so. He literally missed killing Shrek by a hair and would have won the crown permanently. If he did that much damage in a day, what would he have done long term to the people of Far Far Away?
And to the princesses who rose against him. Especially Fiona, who was pregnant with Shrek's children. Who knows what Charming might have done to her and to their triplets?
After Harold finally kicks the bucket, Shrek seems genuinely upset that he's gone, and even sadly calls him "Dad" for the first and last time. Given how Shrek's biological father supposedly tried to eat him as a child, the fact that Harold was willing to extend genuine love for him is the closest Shrek's ever received some kind of paternal love...and then it's gone before he could truly come to appreciate it.
