Isn't there a near impossible way to dodge the blue shell? I thought there was...
Dodging a Spiny Shell
Mario Kart DS
In Mario Kart DS, there is a trick you can learn that will allow you to dodge Spiny Shells nearly every single time you encounter them. The only real limitation is that you must be able to powerslide, which might not be practical on some parts of certain tracks. Also, you must be playing on 100cc or higher (which includes Wi-Fi).
Dodging shells will be much easier if you have prior knowledge of the shell's existence. If you don't know the Spiny Shell is on the field until you hear it hissing then you'll have to be much quicker to dodge it. Make a habit of scanning the item list on the bottom screen often so you'll have time to prepare after seeing an opponent launch it.
When the shell finally reaches you, it will hover over your kart for about a second, then spin over your head once, and then finally drop quickly and explode. Timing is absolutely crucial here, so pay attention. By the time the shell is hovering over your head and starts spinning, you should have red sparks. As it finishes the spin, it will pause for a split second in midair before it starts to drop. At this point, turn hard in the direction of your powerslide (so if you were sliding to the left, press left to make your turn tighter). Just as the shell drops, release the powerslide and immediately start a new one in the same direction. If done correctly, the speed boost from the mini-turbo combined with the extra hop from the second powerslide will cause the shell to miss and explode harmlessly behind you.
It takes a fairly good amount of practice to be able to pull this off for the first time, and even more practice to get to the point where you'll dodge them without fail every time, but it's totally worth it and it helps a lot in getting 3-star rankings in GP. Check out the video to the right for a more detailed tutorial.
An easier way to dodge the blue shell is to get out of first place before it enters the touch screen.
Mario Kart Double Dash!! and Mario Kart Wii
In Mario Kart Double Dash!! and Mario Kart Wii, it is possible (though difficult) to dodge a Spiny Shell provided you have a Mushroom handy. Just as the shell drops (you literally have just a few split seconds) activate the mushroom. If your timing is right the shell will miss and explode harmlessly behind you, as seen in this video. Unfortunately, it is very rare to have a mushroom in first place, so this trick is of limited usefulness. If this is the case, you might as well take a couple opponents out with you. When you hear the siren, check your rear-view camera and brake and/or swerve to get near one or more opponents. Hopefully they'll be inside the blast radius when the shell takes you out. In Mario Kart Double Dash it is not so smart. In the Rainbow Road, the Blue Shell will sometimes miss and will explode behind you without harm. In Mario Kart Wii, the Blue Shell might also miss you when you enter a cannon in Maple Treeway, DK Summit, Rainbow Road, or DK's Jungle Parkway, provided you entered it at the right time. If the shell continues to make the sound while you are in the cannon and it doesn't explode behind you, you have timed it wrong and the shell will come back for you, although it takes a long time, considering that the distance between the cannon and the destination is usually long.
http://mariokart.wikia.com/wiki/Blue_Shell