This article contains plot/ending details.
The Extra Life is a seemingly silly item that Scott Pilgrim picks up at the end of Volume 3. It seems like just another video game reference, but one that becomes integral to the story in Book 6. Without the life, the story would have ended with Scott dying then respawning in his own home and would’ve never lead to the reunion with Ramona or anything else that followed.
Sometimes referred to as an "extra guy" or "1-Up," these are found in most video games.
In Book 3, after Scott defeats Todd Ingram with a killer headbutt, one of the items Todd drops along with the usual coins is an extra life. The life's smiling face appears to creep Scott out significantly.
In Volume 5, the extra life logo was frosted on Scott Pilgrim's 24th birthday cake.
In Book 6, Gideon impales Scott with the Power of Love, killing him, then buys a round of drinks for everyone in the club. However, while trapped in his own Subspace and reuniting with Ramona, the item is automatically activated and the pair return to the fight. Oddly, the Extra Life's hairstyle changed to match Scott's new hairstyle.
In vs. the World
In the Movie, Scott receives the extra life for defeating Kyle & Ken Katayanagi instead of Todd Ingram, and like in the last book, he uses his life after being killed by Gideon. This time, though, the extra life warps back to his apartment (more like a checkpoint), with a x2 power bonus right before he sprints off to Chaos Theatre allowing Scott to replay the whole level. (Although, originally it made Scott see Wallace in bed again). Scott promptly wastes Gideon's guards with timely punches and insults on the way inside, and it gives him the opportunity to make amends to his friends and better face his enemies.
In the movie, the 1-Up is in the shape of Scott's sprite head from the Game.
In the Game
Defeating Todd will earn you a 1-up, just like in Book 3, but the player can buy multiple 1-ups in World 1's No-Account Video store post late-fee payment (The Mystical Head) and a secret shop owned by Wallace Wells marked by a star inside the tunnel of the same stage (Tlaloc's Feast).