Just yesterday, I covered a story where comics writer Mark Millar compared putting together a crossover book to "passing a very difficult stool," and that was based on tying together various books and characters. What about cinematically? Director Joss Whedon, long credited as the creative mastermind who's been able to take producer Kevin Feige's master plan and make it come alive, says that Avengers: Age of Ultron has been a bit of a nightmare.