Start a single player game, then activate the following cheats by entering the corresponding codes:
CHEAT FUNCTION - CHEAT CODE God mode - jjgod Invincibility - jjinv All weapons - jjguns Full ammo for all guns - jjammo Sugar boost - jjrush Flight mode; repeat for more versions such as helicopter ears and hoverboard - jjfly Suicide - jjkill or jjk Power shield; repeat for other types - jjshield Level skip - jjnext or jjnxt Fully light level - jjlight Bird help - jjbird Coins - jjcoins Gems - jjgems Quit to main menu - jjending Quit to desktop - jjq Cycle into Spaz, Bird, Frog, Jazz - jjmorph Power-ups - jjpower Pass through obstacles1 - jjnowall Enable several times for autofire - jjfire 16 color mode - jjcolor Make Jazz or Spaz laugh - jj<2 - 9> Suicide - jjd Change controls - jjcpu Talk - jjt
NOTE 1: This code is best used when flying to prevent falling through the ground. Enable after the "jjfly" code is used.
A few weapons can be used in other way. If there are some items in mid-air out of your reach, use the Bouncer to reach them. It has a very long range and knocking down the items is easy. The Freezer can be used to freeze springs and boxes. Frozen boxes will continue to move even after you stop pushing them. Frozen springs will no longer work, allowing you to enter some areas. Dynamite can be used to destroy Buttstomp Blocks, which is helpful when certain areas are normally blocked off to one of the characters. The Fire Gun (not Flamethrower) can go through walls, allowing you to destroy enemies in relative safety.
On the Carrot Juice level in the Formerly A Prince chapter, go halfway through until you get to the first hidden Giant Red Gem. Smash it by shooting it with any gun, then go all the way to the right, where the bouncy thing is located. Do not go on it, or you will go up through the rocks and have to do it again. Continue right until you hit the wall, then run all the way to the left, where you first dropped down to get to the Giant Red Gem. It will be there again, and you can shoot it to get more gems. Go all the way to the right, then all the way to the left again. It should appear again. Repeat this to get as many gems as needed.
Get a bird with the jjbird code or from a cage and have it kill any enemy in any level. After that, enter jjbird as a code for it to go away. When it leaves the screen, switch to any other weapon and shoot at anything on the screen, then enter the jjbird code again. One bird will appear from one side, then two or three seconds later, the original bird will return. You might not be able see it. However, if you look closely you can see two birds' wings flapping. This may require some practice. You will have to do this every time you want two birds.