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

Pipe Wielder (5 points): Wield the pipe in single-player or co-op mode.
Knife Wielder (5 points): Wield the knife in single player or co-op mode.
Psycho (15 points): Kill 10 enemies without losing your weapon.
Perfect Boss (10 points): Defeat the first boss without dying.
Fourth Boss (10 points): Defeat the fourth boss.
First Versus (10 points): Defeat another player on Xbox Live in a versus match.
Online Warrior (5 points): Defeat 10 opponents on Xbox Live in versus mode.
Online Co-op (10 points): Complete an online co-op game.
High Score (25 points): Score 800,000 points in one game with Game Settings set to Hardcore.
Kill Jet (30 points): Defeat the Boss "Jet" at the end of Stage 2 with Game Settings set to Hardcore.
Hard Win (35 points): Complete the game without using a special attack.
Perfect Win (40 points): Complete the game without continuing.