Um Jammer Lammy Codes -

Bonus Parappa levels:
Successfully complete the game, then return to the level selection screen. Press Right until the bonus Parappa levels appear.

Parappa and Lammy two player levels:
Successfully complete all of the bonus Parappa levels.

Customized lyrics and notes:
Load the game, then immediately reset the PlayStation when Lammy appears at the title screen. Allow the game to reload, and a new menu will appear next to Lammy's guitar at the title screen. Use those options to customize the lyrics and notes.

Special menu:
Successfully complete all levels in the game, including the Lammy and Parrappa levels and the versus levels in one player mode. Select the "Special" option at the title screen to display a new menu that allows all music (Cool, Good, Bad or Awful) to be played while all game characters are dancing under your control. Note: If you complete all the levels but do not unlock the option, finish level 7 with Lammy again.
2-Player Lammies:
Complete any two stages in the normal game to unlock the "2-Player Lammies" option.

Play as Parapper:
Complete the one player game as Lammy to unlock the "Play as Parappa" option.

2-Player vs. Lammies:
Complete the 2-Player Lammies game to unlock the "2-Player vs. Lammies" option.

2-Player Lammy Parapper:
Complete the one player game as Parapper to unlock the "2-Player Lammy Parapper" option.

2-Player vs. Lammy Parapper:
Complete the 2-Player Lammy Parapper game to unlock the 2-Player vs. Lammy Parapper option.

Play against yourself or share a controller:
Complete both the team and versus level of the desired type of game. For example, complete Lammy Rammy team and versus on stage 7. Select that same team or versus level and a "Manual Controller 1" option should appear under the "Manual Controller 2" option. This allows you to play as Lammy and Rammy or Lammy and Parappa.