I came across this jataka (Mahā Ummagga Jātaka):
I never saw a very lengthy jataka before, I found the story very epic. It has unbelievable plots like other jataka but it's still a great story to read. One complaint from me is the english translation that very hard to understand, I can't blame much as it's from an old publication. I hope someday I can see a modern english translation. I also think this jataka can be made into a movie too
I wonder if there are any other jataka with almost same length like this jataka. The second one I can think is Ghata Jataka (Andhakavenhu Putta).