Continuity mistake: In the British Museum, when Rick and Ardeth are saving Evie, Rick gives her a .45 pistol and they start to shoot the guards, her pistol fires once and the slide locks back meaning the pistol had no ammo, but she keeps firing as if the magazine was still full.
Factual error: When Brendan Fraser & his son are running to reach the pyramid before the sun hits it, the sunrise line approaches the pyramid along the ground, but the sun would naturally have hit the pyramid at the top first and worked its way down to the ground. [Some people insist on trying to correct this - think of it this way. If the sun's illuminating the ground from way up in the sky, what's keeping something higher up than the ground in darkness?]
Continuity mistake: When Rick is trapped in the bathroom, he finds John underwater in a bathtub full of suds. As John climbs out of the tub, his body naturally is covered in suds. However, when he and Rick jump out the window and start running away, John's body is completely suds-free.
Continuity mistake: When Rick and Ardeth Bay save Evie from the warehouse after Imhotep is resurrected, there are four mummies chasing them when they get on the double-decker bus. Rick shoots one of the mummies and "kills" it. He shoots another one in half and goes to the top of the bus to fight another one. The top portion of the mummy that got shot in half then fights Ardeth Bay. Evie kills the mummy that got shot in half and the top part of the bus gets torn off by the bridge and kills the mummy Rick is fighting. John stops the bus and they all sign with relief. Whatever happened to the fourth mummy chasing them?
Plot hole: The timeline is off. Mummy started in 1923, yes, but it wasn't until three years later in 1926 that Evie and Rick actually met. Mummy Returns takes place in 1933 - only 7 years later, but they've got an 8 year old son. At that, Rick and Evie's son was born the year before they met...
Continuity mistake: In the beginning when Brendan Fraser is looking around the tunnels he turns around to see his kid and they scream. As they are screaming they are at eye level but when a few seconds later when they are standing the kid is like 2 feet shorter then Brendan Fraser, and if you look around there is nothing for the kid to have stood on.
Continuity mistake: Before Fraser and the gang reach the Oasis, the falcon is sent back to the human army that is advancing in order to stop the Anubis horde. There are literally tens of thousands of men advancing. Yet after the first battle with the Anubis warriors, the human force is decimated. Only a ragged line of warriors remains for the final charge of the Anubis warriors. But there are no human bodies or horses in the sand.
Continuity mistake: In the first movie, Rick (Brendan Fraser) has a tattoo of the eye of Horus on the back of his right hand (easier to see in the theatres than on the video, but if you look closely you can see it several times throughout the film). However, in the sequel the tattoo is gone and now he has that tattoo on his forearm, which he didn't have in the first one. Considering the time period, tattoo removal wasn't possible.
Continuity mistake: During the first battle, the Scorpion King is fighting with his sword in his right hand and his shield in the left. For one instant, they change arms. I assume the film must have been reversed.
Continuity mistake: During the ride on the double decker bus. Rick is fighting the mummy by punching him in the face. The mummy's tongue and face are a grey color. Right before the mummy gets killed on the low bridge we cut to his expression and his tongue is pink.
Revealing mistake: In the British Museum after O'Connell frees Evie from being sacrificed, they both shoot at glass containers filled with alcohol and formaldehyde. Right before they explode, you can see protective masks very clearly on the guards that were standing in front of them.
Audio problem: When they arrive at "The Magic Carpet" you can hear Izzy drag three heavy bolts across the door, when the door opens, there are no bolts - just as well, otherwise shooting the lock wouldn't have worked.
Plot hole: The mummies that attack during the scene on the doubledecker bus are supposedly pretty tough and can smash through brick and masonry walls. However, during the fight just before the bus hits the bridge, the mummy fighting Fraser acts like a normal person. The two grapple together, and the mummy has his hands around Fraser's throat and tries to strangle him. Not only does Fraser fend him off, he even breaks his grip and dives to the floor before the bridge hits. Pretty wimpy for a mummy that just tore through a steel bus roof.
Factual error: In the scene where the airship has crashed, Izzy uses a modern day fire extingusher that was painted black.
Visible crew/equipment: When Ardeth, Rick and Evie arrive at the first city where Imhotep took their son, Evie is walking through the hall where she had the vision of fighting with Anuk-Sun-Amun in her previous life. As she's walking past/behind a column, you can see someone's head and shoulder poking out from the back side of the column.
Revealing mistake: After Rick and Evie find the bracelet the water starts coming after them. There are then shots of the water and then them running. Finally, they stop and hold each other. Shortly after that the wave comes over them. If you notice right before it hits them, it is their doubles you see. Not the actors.
Deliberate mistake: At the beginning, we see the Scorpion King leading his army into battle. However, despite people being stabbed with swords, and slashed, there is no blood on any of the soldiers, nor on their weapons. Kind of hard to believe war was that clean back then.