Young Neil was originally going to be 9 years old.
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).
Maybe Scott should worry about Wallace peeing all over him, seeing as he shares a bed with him.* No, this isn't confusing Kieran Culkin with his brother Macauley. Kieran played Kevin McCallister's cousin Fuller, who was known to wet the bed.
The DVD contains storyboards and concept art for a very different conclusion to the final battle. Two words: Mecha Gideon
Ramona was originally supposed to fight Gideon during the final battle, but the choreographer determined that having four people fighting in a small arena suspended high in the air was too dangerous, so Ramona spends most of the fight on the sidelines.
Word of Saint Paul: In commentary, Aubrey Plaza, who plays Julie, asserted that her character had (and possibly has) an unrequited crush on Scott, which is why she's so hostile to him. While Bryan Lee O'Malley, the creator of the original Scott Pilgrim comics, responded that Plaza was "making shit up", Edgar Wright, the director of the film adaptation, supported this view.
An odd fact mentioned in the making-of documentary. The studio originally wanted the film to be shot in New York, Edgar Wright had to insist on using Toronto. One of the producers mentioned that normally, anything that identifies Toronto as Toronto has to be avoided when normally shooting a movie in Toronto, but here they could go nuts in shooting these locales. And they did.
Ellen Wong, the actress who plays Knives, is actually a few years older than Michael Cera.
This movie has caused Michael Cera to turn himself into a real life example of Crouching Moron, Hidden Badass. He underwent martial arts training for the film's fight scenes and enjoyed it so much he started training for real. He still looks like a complete wimp, but nowadays he's a complete wimp with a black belt.