Scott Pilgrim uses a lot of VFX to portray the Computer Game feel that was prevalent throughout the comic series it is based on, by Bryan Lee O'Malley.
Double negative handled the majority of the combat and on screen effects
The scene where Ramona Flowers is skating through the snow and the snow is melting as she skates over it, the clean plate had an area of no snow where she would skate. The snow was added digitally with spray simulated for where he skates were. Additionally, the roofs of the houses had no snow on them, but with the scene taking place the morning after a snow storm, they added snow digitally.
In the Matthew Pattel fight, Pattel was filmed on a blue screen in a harness, as a lot of his fighting is the manga-style mid air combat. This also allows him to be shot through the air in all manner of crazy spins that would not be possible otherwise. Physical lights were in place for the connection of hits which would emphasise the combat. Triggers would be placed on set which the actors would punch. This would ensure the timing would be perfect. These were composited out.
In the final composite put together by Ian Copeland there are Handrawn flash frames during the impact flashes, these were provided by Oscar Wright, the film’s concept designer.
In another action shot Patel runs across the stage at Scott during which the proportions of the room stretch and distort as they do in Manga animation, in the finished shot the camera appears locked to Patel’s legs as he runs. To achieve this "we shot Patel on a blue jogging treadmill to capture a “camera locked” aspect on his running legs, we then shot Scott, Kim, Stephen and Johnny stills on the Rockit set with a dolly move ."
Fighting Lucas Lee and his stuntmen required a CG smashing skateboard, comic book style animated impact graphics and visualised sound effects were all added in the final comp. Scott and Lee continue to face off in a Manga-like fight featuring zooms lines and a digital contra zoom, achieved by shooting tracking plates on set, slow-motion plates of the actors running on bluescreen and the addition of CG environments, 2D graphic sound effects, hand-drawn speed lines and flare elements.
The Lucas Lee Skateboard Scene. The final sequence has matte paintings of the Toronto skyline, CG steps, CG trees, CG snow flurries, CG sparks, lens flare elements, 2D graphics, bluescreen stunt performers, bluescreen actors, CG coin explosions, CG & photographic smoke elements. Chantelle Williams created the CG environment using Maya and Renderman. Steve Tizzard oversaw the creation and compositing of the action sequence
Digital Doubles are used when Scott is upper cutted by the Vegan Superman, Todd Ingram. The model used is not very detailed, only having similar clothes placed on it, as the shot is so quick and you don't see Cera's face. The same is used for the impact in the bin bags. The next shot shows a beaten and bruised Michael Cera in the trash.