You wielded the pipe in single-player or co-op mode.
You wielded the knife in single-player or co-op mode.
You killed 10 enemies without losing your weapon.
You beat the first boss without dying.
You beat the fourth boss.
You won an online versus match.
You have defeated 10 opponents on Xbox Live in versus mode.
You completed an online co-op game.
You scored 800,000 points with Game Settings set to Hardcore.
You defeated Jet and reached Stage 3 -- with Game Settings set to Hardcore.
You beat the game without using a special attack.
You beat the game without continuing.