When Michael talks with Adam, there are two shots where Michael (played by Dylan Stretchbery) looks older in between takes. Those shots were unfortunately missed in 2012 and had to be re-filmed in 2013.
When Pixel speaks with Neyta in her domain, actor Andrew Callis forgot to wear his gloves. It's the only time in the film you see Neyta not wearing them.
When Gabriel is arguing with Adam in the Gauntlet arena, he angrily throws a spear at Guardian. This shot was captured later by a different actor. So, Gabriel's body type doesn't match.
When Michael reads the note his mom left him saying there are leftovers in the fridge, you can see fresh pasta sitting on top of the stove.
When Pixel is standing over Adam as he is strapped to the table, actress Kelly Rogers didn't wear heels as her character was previously shown she had on. Sound effects of her heels were added in post.
Suriv and Guardian are standing in front of a video screen when Lideri kills a replica of Suriv, and the "room" is just a black background.
When Michael takes the Gauntlet console out of the donation's box, he yanks the chord causing the box to fall. The blunder made the final cut.
When Bacillus leaves Suriv's office, you can see a guard following him not wearing the balaclava, thus seeing her ears and hair.
You see what happens to the main characters when the game resets at the end of the film, but you don't see what happens to Guardian.