Continuity mistake: During "Be Prepared", we see legions of Hyenas marching past Scar, casting no shadows at all against the back wall. In the next shot, we see stripes of shadows going past Scar.
Continuity mistake: In the open field where Simba gets scolded by Mufasa, he happens upon a large paw print in the dirt. An overhead view reveals several blades of grass near the impression (on the lower left hand side in particular), but as Simba begins walking once again in the following shot, no blades of grass can be seen anywhere in the vicinity. (00:23:20)
Continuity mistake: As Simba walks along a fallen tree by the waterfalls, Nala pleads with him to overthrow Scar and take his place as the rightful king of Pride Rock. But notice how his posture changes dramatically between shots. Right before Simba snaps back at Nala, his head is hung low enough to the ground so that his entire backbone is visible, but then it's suddenly lifted to an alert position in the following shot. (01:01:35)
Continuity mistake: When Zazu is flying overhead leading Simba and Nala to the water hole, he swoops down and begins talking about their future as a married pair. Initially Zazu's tail is resting near the ground. But from one frame to the next, it's suddenly perched straight up in the air. (00:14:15)
Continuity mistake: In the scene where Simba tries convincing Scar that Mufasa's death was an accident, Simba stands an inch or two apart from Mufasa's left paw. Once the angle changes, Scar reaches out to comfort Simba, but now Simba is positioned closer to Mufasa's face instead. (00:37:55)