Where the book series takes place over a year, the film takes place over a couple weeks.
In the graphic novel series, Scott begins as a 23 year old and eventually turns 24. In the movie, Scott is 22 and because the movie takes place over a shorter period of time, he never has a birthday.
Ramona changes her hairstyle eight times throughout the book series, where in the movies her hair color is changed only three times.
Scott doesn't receive a letter from Patel, only the e-mail.
In the party scene where Scott meets Ramona, he (instead of shaping out her hair) draws a rough doodle when asking Comeau about her. The picture was actually drawn by Bryan Lee O'Malley.
The scene where Scott urinates and his Pee Bar depletes is now in one of the dream sequences, instead of when he was at Sneaky Dee's (a place not in the movie). Also, the Pee Bar's design differs from the movie and comic. In the comic, it simply reads, "Pee", and it is longer and is designed to look more like a bar from a retro game. In the movie, it reads, "Pee Bar", and it is smaller and is just a simple yellow bar.
In the book, Young Neil explains to Knives that he is just Stephen's roommate and does not play an instrument. In the movie, when asked the same question, he gets confused and starts naming the video games he plays instead.
During the first evil ex battle, Matthew Patel originally had the line "That doesn't even rhyme!". In the movie, Scott says this.
Patel's loss is less humiliating in the movie. Instead of being an easy win for Scott, Patel actually gives Scott a run for his money before being defeated (he actually lands several punches on Scott).
Scott's friends don't help him out in his fight against Patel, as was shown in the comic.
During the fight between Scott Pilgrim and Matthew Patel, Scott's friends are surprised by Scott's ability to fight. In the book, Scott's fighting skills are already known to his friends.
Crash and the Boys are actually incinerated in the movie by a stray fireball from Patel. As such, they do not return in volume 3 as The Boys!! and Crash! to assist Scott.
Patel drops $2.40 instead of $2.10 in comic.
After the fight against Patel, Scott was seen talking to Ramona on a bus when she told Scott about her exes. In the comic book this took place on the TTC subway, presumably Yonge line northbound as its destination reads Finch station.
Knives Chau dyes part of her hair red in Book 2. In the film, she dyes part of her hair blue to match Ramona's.
In Book 2, Knives fought Ramona for the first time in a reference library. In the movie, they only fought in the Chaos Theatre during Scott and Gideon's battle.
Lucas Lee in the books was a decent guy who didn't strive for the defeat of Scott. In the movie he is more of an asshole, never giving Pilgrim the break he offered, instead tricking him into letting his guard down so he could punch him.
Scott's fight against Lucas Lee started with a battle against his stunt doubles in the movie, but Lee still does the dare.
After Todd starts fighting Scott, he throws Scott through the wall of Lee's Palace into the back alley, and after a brief scene, the vegan police immediately arrives and strips Todd of psychic power, ending the fight.
The backstory behind how Scott and Envy met was removed.
Honest Ed's is in the movie, but can only be seen in the background in Pizza Pizza after the fight with Todd Ingram
The Vegan Police are introduced in a different way. Scott tricks Todd into drinking a cup of coffee containing half and half, which then causes the Vegan police to come crashing through the wall of Lee's Palace to remove his Vegan powers.
Scott tricks Todd into drinking half-and-half. In the book, Todd drank it on his own knowingly.
In the movie, Roxie's name is spelled Roxy, possibly a reference to her being the 4th evil ex (Roxy is 4 letters).
When Scott finds out about Roxie and Ramona's relationship, we see a meter in his head which goes from, "No clue" to, "Gets it". In the comic, a baby chicken hatches from his brain when he finds out.
Part of the fight against Roxie involved Ramona controlling Scott's movements to attack. This was based off a 2006 FCBD (Free Comic Book Day) comic involving poster copies of movie star Winifred Hailey.
Roxie does not explode into little furry creatures like the series, instead bursts into coins.
Scott meets Roxie (evil ex number four) for the first time in the movie before fighting Todd (evil ex number three).
In the movie, Roxie was defeated after Scott poked the back of her knees. In Book 3, he does the same thing to Envy, except only paralyzing her. Also, the battle with Roxie occurs at the after party for the The Clash At Demonhead show.
Instead of fighting Envy with a hammer, Ramona uses the hammer to fight her evil ex Roxie.
Scott's fight with the twins is a music battle, with Sex Bob-Omb fighting the twins' electronic music project.
The twins don't speak, either. (this is due to the fact that the actors don't speak English).
Scott's battles with the twins' robots are also omitted from the movie.
In the movie, the twins summon two dragons when playing, and Sex Bob-omb summon a Yeti, something which did not happen in the comic.
In Book 5, Ramona confronted Scott about whether he cheated on her with Knives or vice versa. In the movie, Scott accidentally blurted out that he cheated on Knives with Ramona.
Gideon never steals the Power of Love from Scott. Instead, it breaks and Scott (instead of getting The Power of Understanding like in the comics) gets a different sword called the Power of Self-Respect, which also breaks during the fight.
In the movie, Scott came to terms with his own faults and thus decides to fight for himself against Gideon, gaining the sword "Power of Self-Respect". In Book 6, he admitted and understood that he was no better than Gideon in terms of relationships, thus earning him the sword "The Power of Understanding".
Gideon doesn't have his backup katana hidden inside Envy's dress. Instead he uses a seven-seal hand technique to summon it.
There is no mention of Gideon tampering with Scott's memories.
Scott and Negascott's fight doesn't happen and Negascott appears after the fight against Gideon but even then, the two get along. Their fight seems akin to fighting games in which after facing the last boss you then 'face yourself' by then fighting a clone of your character, which is different from the purpose of their fight in the comics.
In Book 6, Ramona was absent during the fight between Gideon and Scott, until Scott was revived due to his Extra Life. In the movie, Gideon held Ramona hostage via the mind chip, luring Scott to the final battle.
In the movie, Ramona knees Gideon in the balls whilst saying "Let's both be girls." In the books, it is Envy who does the same exact thing to Todd, whilst Ramona never does this.
In the climax of the fight against Gideon, Scott and Knives defeated him in the movie, rather than Scott and Ramona doing so in Book 6.
In the original version of the film, Scott actually ended up with Knives instead of Ramona. This alternate ending was scrapped because of Bryan Lee O'Malley's decision to end the story with Scott getting Ramona, rather than his original plan to have Scott end up alone. Ramona is also somewhat colder in the movie, so that viewers would sympathize more with Knives, and thus accept the fact that it was her he ended up with. But in the final version Scott ended up with Ramona nontheless.
Joseph doesn't appear in the movie and thus there's no relationship between him and Stephen Stills.
The Glow from volume 6 isn't mentioned in the film. Also the details about Subspace are quickly mentioned when Ramona delivers Scott his package, and they flirt with going through Subspace a few times in the movie, but it is not entirely explained nor used as any plot points like it is in the comics.
The Subspace Suitcase is not explained either. The only thing we see about the Subspace Suitcase in the movie is just Ramona pulling her hammer out of there.
In the movie Gideon bursts into 7,000,000,000 coins instead of 7,777,777 coins.
In the Movie, instead of using "The Glow" to tamper with Scott's and Ramona's emotions, Gideon uses an electronic device stuck to the back of Ramona's neck.
Gideon, the cat that Ramona owned that ran away in Book 5 but Scott found and kept is never mentioned or seen in the movie. He has a quick cameo on Scott's mug of cocoa, but that's it.
When Gideon impales Scott, he does not bleed at all, whereas in the comic, he does.
When Scott comes back using the 1-Up he got earlier, instead of immediately coming back to where he was when he died, he has to start over from the part where he got the 1-Up (although it is fast forwarded to the beginning of the fight).
Wallace & Jimmy's kiss took part after Crash and the Boys played Last Song Kills Audience in the books. In the Movie, they kissed after Scott defeated Matthew Patel.
In Book 4, Roxie's ambush took place at night while Scott is leaving his new job. In the movie, it takes place in the daytime and the subplot of Scott getting a job is not used.
The fight against Todd takes place over several days in the books, including their first meeting, the battle at Honest Ed's, and their final battle at Lee's Palace. In the movie, it takes place through all the evening they first meet.
Lynette has no significant role in the movie. Thus Todd never cheats on Envy.
Envy's role is much shorter in the movie then the books. She is never seen again after Todd is beaten, meaning she has no ties with Gideon and isn't present at the final battle. She is also portrayed as much more of a villain in the movie, and her break-up with Scott was simply brutal and not mutual at all, like Scott originally thought it to be in the books.
In the movie, Kim never moves to a new apartment, or back to her parent's house. Scott also doesn't go to visit her on his "wilderness sabbatical," which also didn't take place.
Knives does not turn 18 or graduate from high school.
The entire beach party chapter isn't in the movie, and as such, Kim and Knives don't make out drunk.
Julie doesn't throw tons of themed parties in her "amazing apartment" which is never mentioned.
Young Neil does not get isolated from his friends like in the books, and his break-up with Knives never seems to happen.
Mobile, Wallace's boyfriend, isn't seen in the movie. Instead, Wallace's boyfriend is Other Scott.
Wallace does inform Scott that he wants him to move out, but Scott never leaves to go stay at Stephen Stills', Lisa's, etc.
Instead of the custom drawn icon for the extra life in the book, the film adaptation uses a sprite of Scott's head from the official video game.
Scott never gets his job at the Happy Avocado in the movie. The place is never mentioned and Dominique, the manager, isn't in the film.
Scott and Wallace never have rent problems or have to deal with their landlord, Peter