Shell 2 in Volcano 2 requires you to get a score of 40,000. This can be easily achieved if you have the Nirvana board and Z as the character. I abused the stoke moves and also the x button (which makes you hold a move in the air, gradually increasing your points). Try to collect multipliers (x5 especially) before using stoke mode. They are the difference between earning 9,000 points and 15,000 in stoke mode!