When the gang's boat washed up, Daphne's hair was brown.
When Scooby and Shaggy were being chased by the sand spirit they were wearing baseball clothes, but a close-up of them cowering by a pillar shows Shaggy's shoulder with a green shirt. It changes back to a baseball shirt in the wide shot.
Cleopatra's ghost's eyes keep changing from glowing white to regular eyes. Also, her gown suddenly becomes tattered (like a zombie's) as soon as the golden mask breaks off.
Prince Omar and the dig site would have been surrounded by military personnel in real life, not only because Omar was royalty, but also because the tomb was Cleopatra's. Had Amelia von Butch and her crew attempted to take over the dig in the same way they did in the movie, they would have been immediately arrested, if not killed.
The masked trio who attacked Fred and Daphne in the bazaar were presumably, in order of appearance, Natasha, Campbell, and Dr. von Butch. However, Campbell is very bulky, and being in disguise makes him appear significantly leaner.
The downfall of Cleopatra is shown as taking place in 41 BC. It happened in 31/30 BC.
The pyramids are depicted as being many miles from civilization but they are actually on the outskirts of Cairo, a major city.
Cleopatra's tomb is hidden beneath the Sphinx. This is an unlikely place for her real tomb to be located. By the time Cleopatra was born in 69 B.C.E., the Sphinx and Pyramid had been standing for almost two-thousand years. While there is modern evidence of catacomb-like structures beneath the Sphinx, they're nearly impossible to get into. In Cleopatra's time, these catacombs (if they truly exist) would've been forgotten and both the Pyramids and the Valley of the Kings were abandoned as a sacred burial grounds. Cleopatra's actual tomb was most likely in Alexandria, or a temple near her palace on the Island in which she lived, now sunk beneath the waves.