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

The Big Easy (15 points): Score 1,000,000 points in Arcade Mode.
Happy Medium (15 points): Score 5,000,000 points in Arcade Mode.
Well Hard (15 points): Score 10,000,000 points in Arcade Mode.
Guardian Killer (15 points): Defeat your first Guardian.
Guardian Hero (15 points): Defeat 10 Guardians in a game.
Avant-Guardian (15 points): Defeat 250 Guardians in total.
XXXXX (15 points): Raise the score multiplier to 5x.
The Bouncer (15 points): Bounce 100 enemy bullets with an upgraded shield in one game.
Hunter Killer (15 points): Destroy 20 Hunters in one game.
Bully (15 points): Squash 111 harmless enemies with your ship during one level.
Smarter Than The Average Bomb (25 points): Destroy 50 enemies with one smart bomb.
Grand Master (25 points): Destroy at least 1000 of each enemy type.