Standing at the start of the train and when there's 87 seconds left, when one hears a kankan noise, throw the knife 4 times, and you get an immortal Challenger. Plus, the time freezes while you'll get an extra 10000 bonus points.
If 16 of the same enemy are defeated, the whale appears. If defeated with a knife, one gets a 1-up (and 10000 bonus points). However, power items cannot be used during that time.