Goofs

In an upside-down billiards bar, when Zoey notices a sliding puzzle, a shot showing the puzzle is flipped horizontally. Also, the shot is not upside-down even though she looks up at the puzzle.

Later, when Mike lifting Zoey to the puzzle, the layout of the puzzle is different from the first appearance, then she gets to the puzzle, the layout changes again.

At 1:31:30 a girl is shown sitting next to the main characters and you can hear a waiter talk to her. It shows the girl coming to sit at the table where she was already at and the waiter keeps walking from the same direction & the suddenly he is across the room. All in the span of 30 seconds.

It is heavily implied that Ben and Jason are given a high dose of DMT in the penultimate room. DMT doesn't have an antidote, and nor would one be required as the effects of inhaled DMT only last for about 15-20 minutes.

The characters remove a block of ice, which is frozen solid, from the water, which is not cold enough to freeze.

The extended ending with Zoey and the Police, lift floor light shows 2, Amanda is told to go to 3. The theatrical version have lift floor light in all three lifts, Zoey's lift showing 3.

In the first room having to fill the glasses with water made no sense. They could have easily placed empty glasses into the holes and set books on top of the glasses.

The final puzzle room (also shown at the beginning of the film) has a code door, where four numbers must be slid into place around a central square. If you look closely, you can see that every movable number (not just the correct ones) is on its own track, separate from the others. This essentially means the puzzle can be solved without taking into account the clues, as no incorrect numbers can be put on the square's corners.

In the upside-down room, when Amanda climbs up to the bar looking for clues or the missing doorknob, she said she found a safe and needed a 4 digit code to unlock it, but there's no way for her to have known how many numbers they would need to unlock the safe; it just had a regular 0-9 keypad on the front, but no instruction as to how long the correct code would need to be. They ended up getting 4 digits from the slide puzzle once Zoey solved it, but Amanda couldn't have known that when she randomly asserted that they needed a four-digit code to begin with.

In the official trailer the winning prize for successful escape is dubbed as $1,000,000 but in the movie it is only $10,000, as can be seen printed on the entry voucher and is stated by the characters when they gather for the first time. Still, the entry voucher with the printed sum of $10,000 is also briefly visible in the trailer.

The watchers have no control over who dies. It is a survival of the fittest test. However, the 4th room can only be solved by Ben as it relies on his knowledge of American Sign Language. Had he died earlier, the game would be unwinnable, rather than survival of the fittest.

When speaking with her roommate in the dorm room, Zoey pronounces Leonhard Euler's surname as "YOU-ler" rather than "OY-ler", a name any physicist or mathematician or student of those fields would know very well.