Scott's Bass actually belongs to Scott's younger brother Lawrence West, who loaned it to Scott for an indefinite amount of time. It is a Rickenbacker 4001C64 as the picture indicates. Scott uses it throughout most of the series to play for his band Sex Bob-omb during live performances or band practice. Occasionally, though, he has had to use his bass as a weapon.
In Scott Pilgrim & the Infinite Sadness, Scott beats Todd Ingram over the head with his bass after Todd uses his vegan-powers to attack Envy Adams. This initiates a Bass Battle between Scott and Todd, in which the two bassists use their instruments to create weaponized musical sound waves. Then in Scott Pilgrim vs. the Universe, Scott uses his bass to destroy The Twins' Second Robot at a concert. Unfortunately, the bass breaks in half, leaving Scott without an instrument.
Later, Lawrence comes to retrieve his bass. Scott sheepishly returns the bass in its case. Lawrence leaves with his bass, unaware of its condition.
In vs. the WorldEdit
In the movie, Scott's bass is a model 4003, another model of the 4000 range. He uses his bass to battle Todd Ingram in a Bass Battle. Todd proves to be a better bassist and - combined with his vegan powers - defeats Scott, blowing him away with the power of his bass solo, which also breaks the guitar. Fortunately, the Vegan Police show up shortly after and strip Todd of his Vegan powers, allowing Scott to defeat him.
After it was destroyed by Todd's powerful psychic attack, Scott crudely repairs it with duct tape. Despite its poor condition, Scott was still able to play it and Scott used the bass in the music battle between Sex Bob-omb and the Katayanagi Twins.
In the GameEdit
In Scott Pilgrim vs. the World: The Game, Scott uses his bass in a powerful music attack which is performed when all character use their taunts at the same time. A guitar with the same appearance as Scott's bass also appears in World 3 as a usable weapon and is used in the Bass Battle against Todd to literally attack Todd. Scott is also seen playing it in the end credits, as well as Stephen Stills' ending.