Heres my idea...
Spongebob Squarepants Movie 2: The End Of Bikini Bottom...
The flying dutchmen comes to bikini bottom and threatens to take all of bikini bottom into davy jones locker unless, mr.krabs gives up all his money and prized possesions(spelling?) , knowing mr krabs he says no, so its up to spongebob and patrick to get everything that the flying dutcheman wants before their time is up. if they dont finish the list, it can be the end of bikini bottom as they all know it.
i know its not that good and its similar as the first but im not very good at writing but i am anxious to read your ideas!