Level and Lives Select - Go to the main menu. Hold down (A) + (B) on controller 2 while selecting Options. You can now select how many lives you start with (up to 9), choose your starting stage, and play at the Very Easy and Mania difficulty levels.

Same Character in 2 Player -
At the title screen hold Right and B on Controller 1 and hold Left and A on Controller 2. Press C on Controller 2 with everything else still held down. Now both players can be the same person in 2 Player!

Complete each achievement to get the allotted gamerscore.

First Versus (10) Beat another player on Xbox Live in a versus match.
Fourth Boss (10) Beat the fourth boss.

Hard Win (35) Beat the game without using a special attack.
High Score (25) Score 800,000 points in one game -- with Game Settings set to Hardcore.

Kill Jet (30) Defeat Boss 'Jet' at the end of Stage 2 -- with Game Settings set to Hardcore.
Knife Wielder (5) Wield the knife in single player or co-op mode.

Online Co-op (10) Complete an online co-op game.
Online Warrior (5) Beat 10 opponents on Xbox Live in versus mode.

Perfect Boss (10) Beat the first boss without dying.
Perfect Win (40) Beat the game without continuing.
Pipe Wielder (5) Wield the pipe in single-player or co-op mode.
Psycho (15) Kill 10 enemies without losing your weapon.