Accomplish the indicated achievement to get the corresponding number of Gamerscore points:

Kicking the tires (5 points): Complete the Single Player tutorial mission.
Mr. Awesome (15 points): Defeat the Awesomeland End Boss.
Sal (15 points): Defeat the Gastown End Boss.
Semi Slapshot (15 points): Defeat the Coal Harbour End Boss.
Alex Alternator (15 points): Defeat the Motordome End Boss.
Petrov Piston (15 points): Defeat the East District End Boss.
Cletus Clutch (15 points): Defeat the Wetlands End Boss.
Ricky Bricktop (20 points): Defeat the Downtown End Boss.
Bling bling (25 points): Achieve all gold medals for all Single Player missions.
King of the Hill (20 points): Win first place in an Xbox LIVE King of the Hill match.
Dominator (20 points): Win first place in an Xbox LIVE Race match.
Scrap Yard (20 points): Take out 20 or more opponents in an Xbox LIVE Derby.