Fan Animations
 

This, for example, is one of those fan-animated shorts that are so show-close that it's almost indistinguishable from DHX. Amazing stuff, I think Double Rainboom might have some competition.

I won't post the actual videos to these fan animations for 2 reasons (NSFW and laziness) but they are Epic Pie Time and the .mov series (Apple.mov and the rest)
Epic Pie Time is close to the actual art and even Pinkie's voice is similar. Probably one of the funniest things I've seen on YouTube in a loooong while.
For the .mov series, while the art is completely different, it's also hilarious and I think SUPPOSED to be about the Elements of Harmony vs. Discord gone horribly wrong. Because I just see it as a random comedy.