For winning the last race in career mode. Unlike the others, this one is only 2 laps, but they're much longer, going through many of the previous areas. It's actually pretty easy, even in your first career without being fully upgraded. Focus on attacks when behind, and defensive powerups when in the lead. You can actually rerun this race after even if you win, if you want to grind out money for upgrades. If you lose, make sure to hit retry.