Revealing mistake: I can go with Alex making sandcastles to let his parents know where to go, but if you pay attention, the scale in each castle is perfect in every detail, and there are portions which would just be too hard to make by hand.
Continuity mistake: When Spivey is "sucked dry" by Imhotep, you can see his face is totally decimated. Yet, when Anck comes in later, his face is totally intact, with only a gray discoloration. An easy way to see this is to look at his lips: as he gets killed, they curl and rot completely off, but they are perfectly present on his corpse.
Continuity mistake: In the scene where Rick and Eve are hanging from the bars in the flooding tunnel she has her green top on. The water hits them and then they are haning from the bars, but the green top is gone. Then, when the wall breaks and the two of them spill out, she has her green shirt again. (00:16:15)
Continuity mistake: When Patricia Velasquez has her first flashback to her past life, she is in a room with Imhotep. If you look closely at her shoulders in an up close shot, her hair is in front of both of them. Then we cut to a shot of the room from outside (we can see the room through the balcony) and the hair is still over both shoulders. Then we cut to another up close shot of Patricia, and we see that her hair is over her left shoulder, but behind her right one. (00:49:15)
Continuity mistake: When Evie gets stabbed by Anck-su-Namun, she falls to the ground with her hands clutching the wound on her stomach. Her hands do not leave her stomach (even though her arms are out of the shot, her shoulders stay still) but in later shots her arms are spread out, away from her body.
Continuity mistake: Right after Alex scares Rick, we see him holding a stick with fire on top. Every time they change camera angles the amount of stick between his hand and the fire changes dramatically. Its not possible to make the stick move up and down that fast with one hand without hurting himself. (00:06:15)
Continuity mistake: When Alex is taken on the train, Anuk-su-Namun puts her hand under his chin and kisses him, but when the camera angle changes, her hand isn't under his chin. (00:49:00)
Factual error: In the beginning when Anck Su Namun is holding the black snake and says "Egyptian asps are very poisonous." The snake she is holding is a Mexican Black King Snake, a species native to Mexico and commonly kept as a pet in the U.S. (00:26:30)
Factual error: In the bus chase scene the 'prewar' bus has fleetnumber LT1097. Actually it's a postwar RT-class AEC Regent III bus built circa 1950. Although the LT class AEC Renown was a prewar class of London bus, these had three axles, two at the back. And - for the record - LT1097 did exist, but it was a 'Scooter' type single decker. (00:42:55)
Continuity mistake: In the first movie Ardeth Bay has tattooed on his forehead a bunch of hyroglyphs, one of which is a half moon shaped heiroglyph, but in this movie he is missing the half moon shaped tattoo. (00:29:10)
Continuity mistake: When Imhotep is hanging off the ledge at the end, he yells to his woman to help him. After she leaves, he starts to cry. They show him crying and hanging on with his right forearm on the ledge, then it cuts to a shot of Rick and Evie, then back to Imhotep, but now he is using his left forearm to support himself. Potentially he could have swapped arms, but he doesn't show any sign of having shifted his weight, and it happens really quickly. (01:57:15)
Factual error: The dynamite Rick destroys the log bridge with appears to damage a very localised area. It makes a very narrow, clean cut down the centre, when any explosive you place on a log would naturally cause a wider area of damage to the top than the bottom.
Continuity mistake: In the first movie, one of the canopic jars is broken. In this movie, they are all perfect.
Factual error: During the vision of killing the pharaoh Seti I, When Nefertiti called the pharaoh's guards to save him, and after Evelyn jumped off the magic carpet, the guards shout in Arabic " Yalla ya reggala!" This means in English "Hurry up men!" No one in Egypt was speaking Arabic in this period of history. They should had shouted in Ancient Egyptian, not Arabic. (01:11:31)
Continuity mistake: In the scene where Rick and Ardeth are driving up to the museum to rescue Evy it is raining hard, very hard, yet when they get out of the car to strap on their weapons of choice, there is no rain to be found. Not even dripping off the tree limbs. (00:34:40)
Revealing mistake: When Rick realises his destiny to kill the Scorpion King with the spear he backs into the wall with the painting on of a figure with the tattoo on his wrist. We see this is just a big prop because it wobbles as he backs into it, instead of just standing firm like a rock wall should.
Continuity mistake: When Alex is on the scaffolding in the temple, there are the three bandits looking through some old pots and other bits. You see one of the bandits pick up a pot and lean a boat over to the side. When you cut to the scaffolding where Alex is, he does the exact same thing again, he lifts the pot and tilts the boat.