I referring to the 9 challenges that you do to unlock the gold top hat. I was having trouble with the last one, where you have to kill 6 enimies with one giant anchor shot. Well this morning I found out how. Go to chapter 7-Wilikin World and go to the very end of the chapter. When you are battling the chompy mage at one point he sends out 10-15 chompies all in a line. Just shoot you or anchor cannon there and it should be more than enough. Hope this helped!