As soon as Kurt is done sky diving and is on the ground he'll be without his coil suit and sporting his boxer-briefs.
 

A Little Piece of Home
While playing through level 5 take a moment to stop and look through the alien telescope. To activate the telescope you must first destroy the BottRock Generator, and the panel on the ledge above the telescope. Now shoot the telescope lens to move it into a position where you can look through it to see crack animator Russ Rice on the Bioware balcony having a puff with some Conehead visitors.

Drop Camera
Here's a little trick that will make a new camera effect for you to play around with. By holding L2 and R2 and pressing CIRCLE, X, CIRCLE, X the camera will be dropped in place. As you move, the perspective will change like in Resident Evil. To return the camera to normal, repeat the code.

Farting Doc
Doctor Hawkins needs a new diet. At any time while playing the Doctor hold down L2 and R2, and press in on both control sticks. Now you can watch Doctor Hawkins do something Nasty.

Invincibility
If those pesky aliens are giving you a hard time, enter the Invincibility Code and they'll never kill you again. First pause the game. Now while holding down L2 and R2, press up, up, down, down, left, left, right, right, square, triangle, square, triangle, select, and finally start.

King of the Coneheads
In the Spider Room of level 7 one of the Sniper Balls will unleash a pack of Coneheads. Rather than shooting them, just stand around and wait. If you look carefully into the middle of the room while standing on the upper ledge you may just be lucky enough to see the King of the Coneheads!

MDK 2 Development Team are Stars
While playing through level 4 dont forget to take a moment to gaze at the stars in the large arena with the three Poopsy Generators. Be sure to kill all of the enemies in this room first so you can star gaze without getting killed. Now, using Kurt Hectics sniper scope, zoom in on certain special stars in the sky (they are usually slightly pinkish in color). There you will find the crack team that made MDK2 possible gazing back down at you, along with their Wu-Tang Clan names.

Matrix Camera Mode
While the game is paused press L1 and R1. This code removes the Pause Menu, giving you an unobstructed view of the spinning Matrix Camera Mode while the game is paused.

Maxs Slo Mo Mode
Want to check out the fine details in the animation? Slow it all down with Maxs Slo Mo Code. While holding down Maxs shoot button press Maxs equip weapons button three times.

The Hidden Castle in the Sky
In level 7as you are coming out of the tunnel toward the platform with the boss fight you will see two antennas which Kurt can jump up on. This can be difficult, but keep trying. Now turn around and face the tunnel that you came out of and jump to the roof of the tunnel. Now turn to your left and start shooting low at the sky with your Chaingun. You should eventually see your shots hitting something. It is an invisible walkway. Jump down on to it and keep shooting. Keep following the path of ricochet particles until you reach a little yellow square. It is a fan that will take you up to the next invisible walkway. Use your parachute and fly up. It takes quite a while to reach the top of the airflow, so be patient. Once you are at the top, rotate while firing your gun and look for the same ricochet effect and then fly towards it. Follow this the same as before and eventually you will come to the hidden castle. Take a look around the castle and you might discover something interesting.