(at around 51 mins) When Elliot is the basketball player he makes a slam dunk, hangs on the rim and lands on the floor right as the glass shatters. In the replay, the glass shatters while he's still hanging on the rim.
(at around 1h 4 mins) During the school scene, there is writing on the blackboard. The camera turns away, turns back, and the writing is gone. This happens several times.
(at around 1h 4 mins) In the schoolroom, the Devil erases the algebra assignment (to solve Fermat's Last Theorem). In the next cut to a long shot, the Theorem is back on the board.
(at around 36 mins) When the three armed men are first seen shooting at Elliot on the helicopter, they are at the entrance to the drug compound, next to the guard shack. In later shots, they are about twenty feet behind the guard shack.
When Elliot is sitting on the beach, the sunset is visible in the background, but one shot shows plain blue sky instead of sunset.
(at around 1h 7 mins) When Elliot becomes Lincoln about to leave for his fateful visit to the Ford's Theater, his wife refers to "Our American Cousin" as an "entirely new play." In fact, "Our American Cousin" was first performed in 1858, seven years before Lincoln's assassination, and the performance which Lincoln saw was the play's thousandth.
In the basketball fantasy the score of the game is 135-85, with Elliot scoring 104 points, yet he also recorded 32 assists, which would make the score be more than the 135, it would be at least 168.
(at around 30 mins) During the drug lord fantasy, when Elliot finds out that Alison is cheating on him, one of the minions mentions ordering double prints for the photos. Elliot yells "Idioto" which is translated "you idiot!". Actually, the correct translation would be "Idiota". This Spanish word does not have gender difference.
(at around 27 mins) During the drug lord fantasy, one of Elliot's random outbursts upon discovering that he can in fact speak Spanish is "Mucho gusto!" The subtitles translate this as "I like it very much," but this phrase is actually an idiom that means "Nice to meet you." ("I like it very much" would be "Me gusta mucho!")
(at around 1h 1 min) When Elliot is in the smart guy scenario, he says that the hypothalamus is the pleasure seeking and primitive part of the brain, but in actuality, it is the amygdala.
(at around 43 mins) During Elliot being sensitive on the beach, Frances O'Connor briefly looks back during the dolphin song at the director, Harold Ramis, due to Brendan Fraser's dolphin noises.
(at around 52 mins) During the courtside interview, several of the fans in the stands are obviously cardboard cutouts.
(at around 50 mins) When Elliot first comes out to greet the fans in the basketball game, someone manages to pass through his (obviously composited) leg.
(at around 43 mins) When Elliot is playing guitar In the beach scene, one of the lower frets is clearly bound by black tape so it will not make sound.
(at around 36 mins) Obvious stunt double: When Elliot jumps onto the helicopter in the drug lord fantasy, we see a glimpse of his stomach that is completely hairless. In a previous scene where he is seen walking down a flight of stairs, after waking up, his stomach is covered in hair.
(at around 36 mins) After Elliot's drug lord alter-ego falls from the copter, the film cuts to Elliot himself, his wish ended, falling through the air and crashing onto, and badly denting, the hood of a car. Unfortunately, as Elliot rolls himself off of the vehicles hood and away from the camera, we see the reinforcing back-brace under Elliot's shirt, which has allowed him to fall and dent the car without injury.
(at around 32 mins) When Elliot, as a drug lord, drives to his "stables," the reflection of several crew members is plainly visible in the black van.
(at around 36 mins) When Elliot jumps onto the helicopter to escape and the shot pans with his arm wrapped around the bottom rails, the camera under the helicopter is clearly visible.
(at around 41 mins) Elliot says that he making a garland of beach plums and then mentions the sunset. They are obviously on the west coast but beach plums only grow on the east coast.
(at around 18 mins) When Elliot arrives at the nightclub "DV8" the building is shadowed by the westernmost portion of the San Francisco Bay bridge as well as an oil refinery. There are no oil refineries anywhere on the San Francisco peninsula and the location in relation to the S.F. Bay bridge would place it at the Embarcadero BART station/ferry building. The closest Oil refinery in proximity to San Francisco is about 20 miles away in Richmond. The club appears to be located near the Shell Oil Refinery in Richmond with an image of the Bay bridge spliced in for effect.
During the Elliot Richards as articulate-published-author fantasy, the hostess of the party would clearly be aware that he was gay, so wouldn't have so forcibly pushed that iteration of Alison Gardner into hitting on him.
At 0:17:15, the Devil offers to give Elliot a ride to his car after they leave McDonald's, which is supposedly parked near the bar where Elliot had been to earlier to meet up with his co-workers, but Elliot is never seen driving his car throughout the whole movie.
In fact, at 1:24:44 towards the end of the movie, Elliot is seen riding a bike to his apartment building instead of his car. No reason is given as to why Elliot's car is never seen.
The basketball game ended with a score of 135 to 85 in the Diablos favor. Elliot Richards accounted for 104 of these points according to his end game stats, and also had 32 assists, which is impossible as it is already more than the 31 points attributed by the other teammates. Also factor in that assists are earned during normal game progression, where you can only score 2 or 3 points per score.
(at around 27 mins) When Elliot is speaking Spanish, he says "Donde esta es la biblioteca," which is grammatically incorrect.
In the 'President Elliot' scene, one of the jokes is that he references things that had not been invented in 1865. Frances O'Connor has small chest tattoo that is visible throughout this scene (and in the 'Sensitive Elliot' scene). The technology to apply tattoos with needles, like the one she has, had not been invented in 1865. Not to mention that is was considered forbidden for people of her social stature to have them.
(at around 59 mins) During the intellectual wish, Alison sees Elliot and asks the hostess who he is. Upon learning it is Elliot Richards, Alison says she has read all of his books. It seems unlikely she would not know what one of her favorite authors looks like.
During the basketball game, they have Jerry's name as Lamar.
When Dan is in the basketball fantasy, they have his name as Lamar.