In Water Splash Boss mode, you need to collect various objects to defeat the crocodile(Croker).
It could be a water balloon, a brick, or a strange-looking purple balloon.
You can have this experience. "I've collected everything, What am I supposed to do?"
In this case, There is something you are missing.
Take a look at the top-left corner of the screenshot below. There is a purple balloon object.
This object can be collected by combining special balloons that appear in the game.