This was compiled in affection for the films and not to belittle the work of the people who made the movie.
There are possibly more lying about, so feel free to submit what you can find! Submissions go to or leave them in the comments.
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Derek and Odette, now married, have moved into the Swan Lake castle, which is the place where Rothbart lived and has nothing to do with either of their original castles.
Possible explanation: They chose to live in Swan Lake castle because it's directly in the middle of their two kingdoms that were combined together after they got married.
Despite numerous mentions that Derek (at least) would become king after marrying in the first film, he and Odette are still referred to as "Prince Derek" and "Princess Odette" in the sequels.
In the first film, Odette appeared to be the only human able communicate with Puffin, Speed and Jean-Bob. In the sequels, not only is Derek able to communicate with Odette as a swan, but he and every other cast member appear to speak to all the animals.
After Bridget sets the flowers on fire, she just throws the torch away. It would have caught fire elsewhere.
In the next scene, the close up shows Bridget has lit all the candles. When the shot pans out as Derek enters, two of the candles are extinguished.
During the close-up of Derek when he tells Odette about the fire, it seems as though Odette is slightly taller than him.
When Knuckles first falls into the stream, it seems as though the stream is extremely shallow, rising only to around his feet. Later when Knuckles reaches up to grab a root, the stream’s water level reaches his waist.
There is no humanly way that Derek was able to push aside all of those arrows successfully.
Possible explanation: Derek is a superhero.
Derek not seem to care about Odette in this movie. All men forget anniversaries on a couple of occasions and I know he was the king but come on! Odette was right when she said "He's not going to change his feet". Derek was so inconsiderate to Odette's feelings.
Rebuttal: I completely agree with this, but I just thought I should state this...It happens. It shows that Derek and Odette's relationship is HUMAN. Marriages get this way. [Usually not the first year, but still.] The couple gets busy with work, things come up, time flies, and before you know it, you're falling apart. Odette should have sat him down and told him how she felt before it got so out of control. I understand that she thinks she was doing what was best for him and the kingdom, but sometimes it really is best to be a little selfish. Relationships have their struggles. You just have to realize what's going on and get back on track. Remember that, while other things are important, it's also important to take time from your busy life now and then and just spend time together. They had a problem that most marriages have, and they got through it like true lovers do.
When Puffin sprains his tail he loses his ability to fly. However, when an arrow is shot through his wing in the first movie, he was still able to fly.
Once again, Odette’s necklace changes length throughout the movie.
The dagger, axe and darts that Clavius has thrown at Rothbart’s portrait keep changing position.
That clown mask Clavius wears is physically impossible.
Explanation: The cartoon laws of clothing, which state that everything, no matter be it clothes, masks or accessories, will fit the character wearing them perfectly. Unless the plot requires it not to.
Alternate explanation: Clavius did work beside Rothbart for a good while. Even though he's not a true wizard per se, he might have picked up a few tricks like helping a disguise to work. The same might be true for Bridget and her dress.
Hot air balloons would not have existed in that age (if we assume these movies occurred in the middle ages).
Clavius shot the ransom note intended for Derek to Queen Uberta’s castle when he could have shot it at Derek's castle Swan Lake.
Possible explanation: Clavius isn't very bright.
The note Clavius shot from the hot air balloon could not possibly have made it all the way back to the courtyard of Uberta's castle, as they were (stated by Uberta) hovering over Swan Lake, which, as seen in the first film, was quite far.
When Clavius and Uberta return to the volcano, the basket/ship is at such an angle, both of them should have fallen out.
As Queen Uberta walks down the stairs with Knuckles behind her, the position of the balloon basket and the bags on it change.
During the ‘That’s What Your Do for a Friend’ sequence, Odette was extremely violent swinging Jean-Bob like that. And he should have flown upwards into the trees, not downwards toward the ground.
Even with Derek gone, there should have been guards protecting Odette in the castle.
Possible explanation: The guards were all out having coffee. At the same time.
When Clavius threatens to lock Odette in the tower, Puffin flies towards her despite his tail still being sprained.
When going after the Orb, Bridget uses a torch to open the secret passageway. Jean-Bob then takes that exact same torch into the passageway with the rest of the gang, causing the door to close, so there is no way that Clavius could have opened the passageway behind them.
Possible explanation: There are multiple torches along the stairwell since you can see the light of at least one other in the near vicinity, perhaps Clavius used one of those.
Addendum: While the above explanation is possible, it would have been better to show this. Various people I know who've watched the movie are confused by this scene and thought that this would be the part where Clavius realises that his plan's been thwarted.
There is no way Bridgett’s hag outfit could fit underneath her pink dress.
Explanation: See the explanation for Clavius' mask above.
During the chase scene there is not a single other person in the castle.
Addendum: It's likely that they couldn't animate too many characters for budgetary reasons, but it's still jarring to see the castle as empty as a tomb.
During the chase scene, the orb hits walls, tumbles down the stairs and performs impossible maneouvers without breaking. Furthermore, it should not have BOUNCED after hitting the chair, at least not that high.
Odette knows the way to Clavius’s castle perfectly when she didn’t even get to see the map Derek was holding for more than a few seconds..
Possible explanation: She has a photographic memory.
In the first movie when Odette was in the form of a swan she wasn’t able to talk to humans, but this time she can.
Possible explanation: Bridget did something differently with the spell this time.
Among the swords that fall around Derek, one falls slightly above Derek’s head, but in the close-up it appears to have fallen directly beside Derek’s face.
When Derek swings on the vine above the quicksand he isn’t holding his bow, but once he falls into the quicksand the bow appears beside him.
While flying, Odette spots Derek’s bow lying in the quicksand, but when she dives in the bow is gone.
After Odette and Derek first climb out of the quicksand they are both covered with the wet sand, but in the next shot all the sand is gone.
In the first movie when we see the Swan Lake castle's dungeon there are two doors, but when the animals are hiding in it, there is only one. Later when the Clavius uses Bridget to lure the animal gang up to the doors, there are two again.
When Bridget tells the animals to bring the orb, Clavius is standing behind her (out of sight of the animals, we assume). When she reels them up, he's gone, only to appear again a second later.
When trapped in the water dungeon, couldn't the gang have just squeezed out through the hole they made in the first movie?
Possible explanation: Odette and Derek had the hole sealed after moving into the castle.
When Jean-Bob, Puffin, Speed and Bridget are trapped in the dungeon, Clavius notices the glowing orb as it is night time, but in the next scene, it's still day/evening of the first day.
The objects in Clavius’ lair keep changing.
When Knuckles begins the rockslide, a giant boulder falls in the valley Derek is walking through. The next time we see that same valley (as the rocks continue to fall), the giant boulder is gone, only to reappear while Derek is swinging.
It should have been impossible for Derek to walk across that rope, especially because it wasn't even a TIGHT rope, but loose and sagging under the weight of the cart.
There's no way Puffin, Speed and Jean-Bob would have been able to pull Derek's weight up the cliff.
Derek’s timing is extraordinarily perfect when it comes to saving Odette from falling.
Possible explanation: SuperDerek strikes again!
Clavius changes Queen Uberta’s gown into a commoner’s outfit during his song, but in the next scene she has her gown back.
Clavius kidnapped Queen Uberta to lure Derek to his lair. So once Derek actually arrives, why is Clavius still so desperate to keep her there?
Possible explanation: Clavius has somehow gained somewhat of a crush on Uberta. Notice how he looked so willing to give her the orb that still had the powers inside.
When Queen Uberta and all the animals enter the balloon basket, Odette is missing.
Derek’s shirt is clearly torn all the way down during the fight with Clavius, but once he is in the balloon basket, his shirt is only torn slightly at the top.
Clavius killed Jean-Bob. The movie offers no explanation, whether logical or magical, why he is revived after the transformation sequence.
Possible explanation: In the third movie we see that the forbidden arts do have the power to revive the dead, at least when they are at full strength. Maybe when Odette transforms back her tears evoke that full power?
In the scene where Odette becomes human once more (and Jean-Bob revives), Derek runs to her, takes her in his arms and spins her around (throwing Jean-Bob to the other animals). This is the exact set of frames from the original as Derek is wearing his quiver, which he did not have during the fight with Clavius.