Continuity mistake: During the interview, while sitting, his striped pants are unzipped for a few cuts, then they are zipped in later shots.
Plot hole: Scar tells the pack he didn't make it to the gorge in time to help Mufasa. However Zazu was with them at at the gorge. He could have easily told Sarabi or any of the other lions on the numerous times he spoke with them, exposing Scar.
Suggested correction: Actually, Zazu wouldn't honestly say that Scar was lying; he left Scar at the gorge, but for all he knows, when Scar talks about not getting to the gorge in time, Scar could just mean that he couldn't find a safe path into the gorge to help Mufasa and Simba escape.
Suggested correction: Zazu wasn't with them when Scar said so. He was with Rafiki. He couldn't have heard what Scar was saying.
Suggested correction: But it wouldn't have confirmed that he killed Mufasa.
It would prove that Scar (who had the most to gain from Mufasa and Simba's deaths) was lying about the circumstances surrounding their deaths. But no-one brings it up.
It would prove Scar is lying about the events of Mufasa's (and Simba's presumed) death, and given Scar gained the most from it, the other animals should be extremely suspicious of him.
Continuity mistake: When Elton and John Reid are kissing in the cupboard John's hand keeps changing between shots. John's hand rolls down Elton's chest, then the next shot it's on Elton's cheek, the next shot he takes his hand away, then the next shot his hand is by Elton's mouth and Elton pretends to bite John's thumb.
Continuity mistake: When Aladdin dances in front of Jasmine his hair keeps swapping between perfectly brushed and messed up.
Revealing mistake: The film was rushed to theaters, leaving a few mistakes which Universal fixed. In the original cut, toward the end, Judi Dench's human hand is visible, complete with her wedding ring. This was fixed for the re-release.
Continuity mistake: When Anna's singing "The next right thing" she puts a bag on her shoulder, with the strap on top of her hair. After the camera spins round her, her hair is suddenly on top of the strap. This bears a strong similarity to the mistake in the original Frozen where Elsa's hair passes through her shoulder - might be a deliberate nod, or else animating hair around objects is difficult enough that shortcuts are often taken.
Continuity mistake: After the cartoon segment, Deni entertains some playful banter with his girlfriend and takes off, putting a shirt on while he runs. When the neighbour asks him "Late again?", the guitar strap is on opposite sides of the instrument as the editing switches to a reverse shot. (00:06:40)
Continuity mistake: When Aunt Sarah arrives, she dumps her luggage in the hands of Jim and then passes him to his right, leaving him between herself and the door. In the reverse shot, Jim is on the opposite side. (00:29:15)
Continuity mistake: After the alien abduction, Emmet plans to lead a rescue mission and opens the gate asking "Who's coming with me?" During the sequence, the shadows change completely. At first he is not casting much of a shadow, then it reaches the metal doors, then it stops midway towards it. (00:20:55)