For Trivia tropes that apply to the film, go here. For Trivia tropes that apply to the video game, go here. For trivia tropes that apply to the anime, go here.
General franchise:
Creator Backlash: O'Malley said the one character he would remove would be Stacey, due to him naming her after his actual sister, or at least give her a different name. She is gradually Out of Focus after the early installments.
Reality Subtext: O'Malley was first inspired to make the comic when he learned that his girlfriend (now ex-wife) had three ex-boyfriends who were all named Matthew, and he wondered if they could form some kind of league. He was also going to name the second ex Matthew Lee, but thought that was too far to go for such an inside joke.
Teasing Creator: O'Malley has said on multiple occasions, that, although the Scott Pilgrim series is done, he's not done with these characters, and has implied several times he may make more books in the same universe, though not necessarily with Scott as the protagonist.
Word of God: O'Malley revealed on his blog that the Evil Exes didn't actually die when Scott defeated them, they were simply zapped back to their homes in the U.S. They decided to give up their vendettas against Scott due to deeming traveling all the way to Canada for something they've already failed at not worth it. This also explains why there are no police in this universe (asides from the vegan kind), since Death Is Cheap is applied.
By O'Malley's own admission, Scott's life is based on the lives of himself, his then-wife, and his peers when he was a young twentysomething. He was in a garage band, obsessed with video games, and fell in love with (and eventually married) an American woman (they have since divorced) who had several ex-boyfriends, including two with the same name, whom he jokingly thought were all in some kind of League together. The concept ballooned from there.
What Could Have Been: There are many cases of this, but most of them are really insignificant.
Young Neil was originally going to be 9 years old.
Volume 3's cover art was going to be the main characters standing in the middle of Toronto, Volume 4's cover art was going to feature Lisa Miller winking in a blue fluffy background, and Volume 5's cover art was going to be Ramona in a pink sweater looking down at the ground on an empty white background.
Deleted scenes include:
For Volume 3: after Lynette punched the highlights out of Knives' hair, Knives had to get medical attention. She was so badly (and socially) injured that a doctor said she'll never be cool again.
At Volume 4 when Wallace and Kim dance in the beach. Kim was smiling.
The amp vs amp battle with the Katayanagi Twins in the movie was supposedly based on an early draft scene of Volume 5.
Also in Volume 5, it was planned for Young Neil to get a bizarre new girlfriend with an incredibly humorous scene, but her scenes ended up being scrapped before they were drawn.
A significantly different version of Scott's brother Lawrence West would have been in league with the twins in Volume 5, according to O'Malley's original version of the book.
Almost certainly a coincidence, Scott is the exact same age as Paramore's former guitarist, Josh Farro. The two have the same birth year (taking into account the implied setting of 2011 for the comic Scott would be born in 1987) and Scott's birthday (9/27) is two days before Farro's (9/29).
In the original pitch, Knives was going to date Stephen instead of Young Neil after breaking up with Scott. Elements of this were carried over to some light Ship Tease between the two becoming noticeably closer before it was revealed that Stephen was gay.
In Scott Pilgrim Takes Off, Stephen and Knives develop a very close friendship and working relationship over the course of the story, but it's never depicted as romantic in any way, for obvious reasons.
that the Evil Exes didn't actually die when Scott defeated them, they were simply zapped back to their homes in the U.S. They decided to give up their vendettas against Scott due to deeming traveling all the way to Canada for something they've already failed at not worth it. This also explains why there are no police in this universe (asides from the vegan kind), since Death Is Cheap is applied.