used in mario kart double dash; allows you to dodge green and red shells. if you're really, really good, then you can sometimes dodge the blue shell. if you know how to use it right, you can increase your lap time and boost around corners with precision! called blue boost because it gives your vehicle a boost and it looks like a blue flame coming from the tires.
Person 1: I just dodged your red shell with the blue boost.
Person 2: Damn it!