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 robotic character Smoke fires a missile that destroys a large structure in the underground cavern during his fight with Lui, if you look closely, when the explosion occurs, you can actually see additional "phantom" debris exploding upwards (from two independent bursts) from underneath the fog in front of the actual explosion, obviously to make it seem more dramatic. These secondary bursts also noticably occur several seconds after the initial explosion.
Revealing mistake: When Sonya grabs Cyrax's back and throws him into the wall (towards the end of their fight), you can see his back, supposedly made of metal (he is a robot), bend like rubber.
Deliberate mistake: When Sonya finishes Mileena, Mileena's shoulders are muddy and she is face down, but when we have a close up of the dragon tattoo the right shoulder is cleaned off and what mud is left is dry. (00:42:25)
Visible crew/equipment: When the purple ninja 'Rain' is smacked into the fire pit by Shao Khan, look closely as the body falls into the pit. A stage helper's hand comes up to catch the falling 'body'.
Continuity mistake: Somehow right after the mud fight Sonya is completely clean and dry minutes later. Yes she said she wanted to find a river and clean up, but her white shirt wouldn't have cleaned like that in a river.
Revealing mistake: When Rayden and Kahn fight at the start of the film, at one point Rayden does a flying body-spear into Kahn, which sends him flying backwards. When he lands on the ground, the floor beneath him "warbles," revealing he landed on a pad. It also continues to move a bit for the rest of the shot as he moves.TedStixon
Revealing mistake: During the opening scene, a few shots after we see the Outworld ninjas falling through the portal and leaping about, there's a shot of several monks fleeing that tilts up towards the (digitally replaced) sky. As it does this, you can see several hard lines about in the sky from where pieces of the digital animated skies were "stitched together." It's easy to miss the first time, but if you know to look for them, they're pretty obvious. You can see similar lines in the sky in several other shots throughout the scene, but it's most noticeable here.
Revealing mistake: During the opening scene, when the ninjas begin to arrive through the portal, in several shots as they leap about, you can tell the stuntmen were filmed in front of a greenscreen and crudely "cut out" and placed over the footage. They're very strange-looking and have a weird jagged border around them. Some of them are also missing pieces of themselves or look like they were improperly "cut out."