The Marvel Cinematic Universe is arguably the most popular ongoing franchise in the world of cinema - having two of the top five highest-grossing films of all time amongst their instalments exemplifies that - and upcoming epics like Guardians of the Galaxy and Avengers: Age of Ultron will surely only serve towards increasing that popularity. The unique nature of its ever-expanding universe is one that means it won't get boring any time soon (which is a relief, given that Marvel have a fourteen year plan of new movies in place already), as Marvel have a near-endless list of characters and concepts from which to pluck ideas for it, with a rich history of stories having been published since Marvel was established (albeit as "Timely Comics") back in 1939. That said, at times, they've done their very best to mess things up with some terrible mistakes. From miscasts and terrible interpretations of characters, and from stubbornness to carelessness, the Marvel Cinematic Universe has almost fallen flat on its face a few times thanks to its errors and, in this article, a number of those instances will be discussed. Here are ten terrible mistakes that almost ruined the Marvel Cinematic Universe for everyone (contains Marvel Cinematic Universe spoilers)...