Revealing mistake: When Fletcher is beating himself up he goes into a stall and squishes his head with a toilet seat. You can see that the white part underneath is made out of foam because it keeps squashing down.
Revealing mistake: At the end of the Sub-Zero vs Scorpion fight, Liu Kang jumps over to help Sub-Zero and Scorpion teleports away. A few moments later you see a shot where you see all the actors, (Liu Kang, Sub-Zero and Kitana), if you look closely you can see Scorpion waiting in the background just waiting to pop up and snatch Kitana.
Revealing mistake: When the monkey points up the hill and Odysseus keeps climbing, modern houses and roads are visible on the ground below.
Revealing mistake: In the end, Phillip lands in the chair and he stops bouncing. You think he would still bounce even though the chair was soft.
Revealing mistake: When the Cyborg Master enters the police station, he shoots two police women before a third cop starts shooting back with a shotgun. The third shot he fires hits the wall behind the cyborg, and the entire wall wobbles as the squib goes off to make the hole in the wall.
Revealing mistake: When Katherine is doing cartwheels, her dress stays down in relation to her feet. It doesn't ride up or flap towards her upper body.
Revealing mistake: During the final battle in hell, when the army of Spawns rise up, there are some small errors to look for. First, during a few shots where the army is closer to camera, you can see the CGI army becoming "pixely." Also, you can see at least one of the Spawn floating in the air, not standing on the platform with the rest of him. Problems with the CGI rendering/animation.
Revealing mistake: After the Djinn escapes and there's an explosion in the lab, you can see some stuff on the ground that looks like it's on fire. The objects are not actually burning, the fire is being produced by a burner. There's no smoke from the objects, which is a dead giveaway that they're not actually "on fire." (00:18:15)
Revealing mistake: At the very beginning of the film, we see the transfer vehicle carrying Jack driving down the road. You can tell in several shots that the (fake) snow isn't really falling, but is just being blown in front of the camera from off-screen, especially since there's no snow hitting the road, and it's coming from the side, not above.