Continuity mistake: When Elliot's the basketball player, when he scores the slam-dunk and breaks the headboard, he breaks the headboard after the slam as he bounces/hangs off the headboard. But in the replay he breaks the headboard as he makes the slam and then bounces/hangs off the headboard. (00:49:10)
Continuity mistake: When the Devil is a teacher in the classroom she is erasing homework assignments off the board. In the close up shots (and maybe 1 or 2 of the far away ones) the board's partially erased. In most of the far away shots however, the board isn't erased. (01:01:50)
Continuity mistake: Elliot is hanging from the trifork in hell, his shirt is smoking and is close to catching on fire. The angle changes and there is no smoke then changes back and there is smoke.
Continuity mistake: When Elliot is this red-haired guy on the beach, he gets his mouth kicked full of sand. But when he stands up one second later and talks to the boys, his mouth is completely clean. (00:42:45)
Continuity mistake: At the beginning of Elliot's basketball player wish, he makes an amazing slam dunk that shatters the glass. Pay attention to the scoreboard before he makes the shot. The final score is displayed before he even score the final points.
Continuity mistake: In the basketball wish scene, Elliot is dancing and celebrating his success when he leans right up to the camera to yell something. When he leans back for a split second his eyes change to blue, his natural colour, then back to brown again.
Visible crew/equipment: During the Basketball wish, while Elliot is being interviewed by the sportscaster, you can obviously see cardboard "people" filling the stands in the background. (00:49:45)
Factual error: When Elliot is the sensitive guy he picks up the guitar to sing a song to Allison. The guitar has a capo on it. During the song Elliot is changing cords and finger placement. He makes a cord above the capo. This would not be possible since the capo effectively cuts off the strings at the point of the capo. Any finger movement above the capo would not change the chord at all. (00:43:00)
Visible crew/equipment: In the wish where Elliot is a drug lord, when he is driving to his stables, in one side shot of the black van you can see crew members reflected in it. (00:31:10)
Continuity mistake: At the very start of the film when Elliot is holding the door open for the people and they start to rush in at a very high speed, if you look closely about halfway through you will see the same people going in like in the first half of it (Especially look for a woman in a light blue suit). The clip is just being replayed.
Continuity mistake: Elliot is given a contract in the Devil's office. In one shot the contract is hanging off of the edge of the table. But a couple shots later, when the Devil picks up an apple and walks by the table, the contract is further onto the table, in a different position. (00:21:20)
Continuity mistake: When Elliot first walks to the Devil beside the snooker table you get a wide shot and you can see all the snooker balls on the table. The position and colour of the balls change in a later shot when the Devil takes a shot and pots all the balls. (00:09:50)
Continuity mistake: When Elliot is talking with his 'buddies' in a bar his shirt collar is hanging over his brown sweater. But in the next shot as he's walking over to Alison, his collar is tucked under it. (00:07:50)
Revealing mistake: When Elliot appears in the fountain, after the sensitive guy segment, water is already up his trouser legs. (00:44:50)
Revealing mistake: In the scene when Elliot speaks Spanish, there's a mix of different Latin American accents, and what he is saying does not make much sense to a Spanish speaker.
Revealing mistake: During the opening sequence we see a lot of things happening very quickly and sped up. Everything is going in a progressive direction, not going backwards. As the sun rises in San Francisco a clock on a building is shown. The hands on the clock are going backwards instead of forwards. This was shot at dusk, not dawn, then reversed. (00:02:25)
Continuity mistake: When Elliot refuses to make his last wish, the Devil extends her hand fully forward to send him to hell. In the next shot from behind her, her hand is raised.
Continuity mistake: When Elliot is on the beach with Alison, we get many shots of the beautiful sunset which continually makes him cry. But you can actually see blue sky behind Elliot as he sits and talks to Alison. (00:39:35)
Continuity mistake: When Elliot wakes up as the Colombian drug dealer he looks over at Allison then at the wedding band on his hand. Then when he walks over to the mirror the wedding band is gone.
Continuity mistake: After Elliot walks out of the elevator after becoming the charming, articulate man, the elevator doors shut twice behind him. (00:55:30)
Answer: It definitely is a Montegrappa Oriental Zodiac pen, this brand has been making pens in Italy since 1912. I am not sure which of the three red pens in that collection (Oriental Zodiac) is the one seen in the movie, but given its association with the devil, my guess will be it is the Ox fountain pen.