The Mistake: One of the undeniable reasons for the MCU's success to date is that it doesn't take itself too seriously, and is largely powered by a sense of fun, accentuated by a ton of hilarious one-liners. However, Age Of Ultron made clear one potential flaw for future movies as the canvas gets bigger: the quips have already begun to feel a bit arbitrary and thrown in for the sake of it, and with so much comic ground already covered, things might start to feel stale by the time Infinity War rolls around in particular. Why It Could Ruin Phase Three: When the real stakes are introduced once The Avengers battle Thanos, fielding out funny dialogue every few seconds might detract from any real dramatic impact. After a point, things are going to need to get a little more serious if Marvel wants audiences to feel really immersed in what's going on, not that Phase Three shouldn't be fun as well. Humour in moderation, perhaps.