Death Jr Codes:
While the game is paused, hold L and R and enter the following:

Down, X, Down, X, Down, X, Down, Triangle, Up, X - Warp to Final Battle stage

Down, X, Down, X, Down, X, Down, X, Up, Triangle - Warp to The Basement

Up, X, Down X, Down, X, Down, X Down, X - Warp to The Museum

Up, Triangle, Up, X, Down, X, Down, X, Down, X - Warp to Basic Training stage

Down, X, Down, X, Down, X, Down, X, Down, Square - Warp to Advanced Training stage

Down, Triangle, Down, X, Down, X, Down, X, Down, X - Warp to Seep's Hood stage

Down, X, Up, X, Down, X, Down, X, Down, X - Warp to The Corner Store stage

Down, X, Down, Triangle, Down, X, Down, X, Down, X - Warp to My House stage

Down, X, Down, X, Up, X, Down, X, Down, X - Warp to Udder Madness stage

Down, X, Down, X, Down, Triangle, Down, X, Down, X - Warp to How a Cow Becomes a Steak stage

Down, X, Down, X, Down, X, Up, X, Down, X - Warp to The Burger Tram stage

Down, X, Down, X, Down, X, Down, Triangle, Down, X - Warp to Higher Learning stage

Down, X, Down, X, Down, X, Down, X, Up, X - Warp to Growth Spurt stage

Down, X, Down, X, Down, X, Down, X, Down, Triangle - Warp to Bottom of the Bell Curve stage

Up, Triangle, Down, X, Down, X, Down, X, Down, X - Warp to Big Trouble in Little Downtown stage

Down, Triangle, Up, X, Down, X, Down, X, Down, X - Warp to Moving on Up stage

Down, X, Up, Triangle, Down, X, Down, X, Down, X - Warp to Burn it Down stage

Down, X, Down, Triangle, Up, X, Down, X, Down, X - Warp to Happy Trails Insanitarium stage

Down, X, Down, X, Up, Triangle, Down, X, Down, X - Warp to Inner Madness Stage

Down, X, Down, X, Down, Triangle, Up, X, Down, X - Warp to Shock Treatment stage

Down, X, Down, X, Down, X, Up, Triangle, Down, X - Warp to Into the Box stage

Up, Up, Down, Down, X, O, Triangle, Square, X, X - Increased Health and Stamina

Up, Up, Down, Down, Up, Right, Down, Left, X, X - Fill Pandora Assist meter

Up, Left, Down, Right, Left, Triangle, Square, X, O, Square - Eyedoors no longer require souls to open

Left, Left, Right, Right, Left, Right, Left, Right, X, X - Free Seep

Up, Up, Up, Up, Down, Down, Down, Down, X, X - Free all characters and unlock all levels(must enter any stage and re-enter the museum for code to come into effect)

Up, Up, Down, Down, Triangle, Triangle, X, X, Triangle, Triangle - Assist Extender

Right, Up, Down, Up, Triangle, Up, Left, Square, Triangle, Right - Widget

Triangle, O, X, Square, Triangle, Up, Right, Down, Left, Up - Big Heads

Triangle, Square, X, O, Triangle, Up, Left, Down, Right, Up - Big Scythe

Triangle, Up, O, Right, X, Down, Square, Left, Triangle, Up - Odd monsters and scythe has trails

Down, X, Down, X, Down, X, Down, X, Down, X - Monsters are different colors and scythe has trails

Down, Down, Up, Up, Left, Right, Left, Right, Square, Triangle - Weapons have different names

Up, Up, Down, Left, Triangle, Triangle, Square, X, O, Square - Attacks have different names

Up, Right, Down, Left, Up, Triangle, O, X, Square, Triangle - Bullet holes become pictures

While Holding L and R, press Up,Up,Down,Down,Left,Left,Right,Right,Square,Triangle - Invincibility

While Holding L and R, Press Triangle,Triangle,X,X,Square,Circle,Square,Circle,Down,Right - Ammo Refilled

While holding L and R press up, up, down, down, left, right, left, right, X, O - All weapons and weapon upgrades

While Holding L and R, Press Triangle, Triangle, X, X, Square, Circle, Square, Circle, Right, Down - Unlimited ammo