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.