Continuity mistake: When the door to Shrek's house is first opened (just after the honeymoon), it opens into the house. Every other time it opens to the outside. It's not a two-way door, because you can hear it hit the doorframe. (00:04:50)
Continuity mistake: When the request is made by the messenger to have Shrek and Fiona come to Far Far Away for the wedding party, as the trumpeteers troop off in the background you can see their footprints on the ground. However, when the same view is shown again seconds later the footprints are gone. (00:07:45)
Other mistake: This is a UK/US vocal talent variation. In the UK version the voice of the Ugly Stepsister is that of UK TV/Radio Presenter Jonathan Ross yet the vocal talents are credited as CNN talk show host Larry King. Also, the voice of the Red Carpet Reporter is none other than UK Pop Idol Extra presenter Kate Thornton, yet again, the voice is credited as Hollywood reporter Joan Rivers, whom the physical appearance of the character is based on. (00:28:20 - 01:03:50)
Continuity mistake: When Puss in Boots plants his sword in the ground then jumps out of his boots, his sword, boots and hat are nowhere near any trees or grass. Yet after attacking Shrek, Puss in Boots lands in his boots, and his boots, sword and hat have moved to being right beside a tree. (00:32:30)
Audio problem: When the Fairy Godmother sings "Holding Out for a Hero" she tells the pianist to 'put it in C minor,' yet the pianist immediately begins to play in G minor, and the rest of the song is sung in that key. (01:08:15)
Continuity mistake: Puss saves the Gingerbread Man from drowning in the castle's moat by catching him with his sword, however, he is on Donkey's back and the drawbridge is a couple of meters above the water. So the sword would have to have been 2-3 meters long to get down to the Gingerbread Man.
Audio problem: When Fairy Godmother is lying on the piano using her wand as a microphone and singing about tossing and turning, sometimes Kyle's hands don't match the sounds of the piano. This is especially visible in very last shot - just before she says "Hit it", Kyle raises one hand and then we hear a part requiring both hands.