It's listed on this page, which incidentally is a good overview of all the game play features:
Quoting that page:
"The [Kraken] battle ends if you lose one or both of the balls but make enough hits to reduce its life bar to zero and you start a 3M hurry up on the same shot, plus you light the Destroy Kraken compass task. Collect it before it counts down to 1M and Victory Jig frenzy mode starts, accompanied by a much more robust "Yo ho, Yo ho, a pirate's life for me" theme than the one at the start of the game. "
What's Victory Jig Frenzy Mode?