YMMV / My Little Pony: The Mentally Advanced Series
Adaptation Displacement: Greg says in this blog entry that this is happening to Rainbow Factory, that an increasing number of people think that Greg created the story, and Aurora Dawn was stealing the idea from him. He attempts to rectify this by linking to the original fanfic, and vowing to credit Aurora the character as Aurora Dawn's creation every time she's used, such as in the short "Investment Losses".
Hell, pretty much any song from this series, as well as a lot of the BGM from Mentally Advanced. This despite Greg's admitted inability to sing. Somehow he still makes it work.
Determinator: Arguably Greg himself. Since starting his series in 2011, he has had to teach himself how to edit (he admits in the first episode he had no idea what he was doing), endured multiple bogus copyright claims on his work necessitating him having to form an LLC and seriously study IP law, nearly lost all his content due to Blip being jerks, faced animosity from other creators and their Fan Dumb as well as apathy from the major fansites, had to retool his series twice to keep the ContentID trolls off his back, ultimately having to take the original episodes down for good, and lost contact with pretty much every other person who provided voices. Oh, and he had to admit that he was unable to complete the anticipated Grand Finale to Rainbow Dash Presents. After Petirep went pro and left Dawn Somewhere, Greg (again with zero previous experience) had to teach himself how to draw and use Flash, but with the trade-off that the series would have to start over from the beginning. Anyone could be forgiven for responding to all that with Screw This, I'm Outta Here!, but Greg is still making new episodes as of mid-2015.
In "Griffon the Brush-Off", Pinkie tries to spray Fluttershy with aqua regia. Aqua regia is a highly corrosive liquid able to dissolve gold and platinum.
During "Winter Wrap-Up", Twilight and Rarity's conversation is derailed by discussion of several words with "hippo" (or "hypo") in them; some of those words are rather obscure.
Twilight's description of the perils of intestinal surgery is scarily accurate.
Twilight says that Apple Bloom was "born from consanguineous mating".note Consanguineous comes from the Latin word for blood, and means "descended from the same ancestor". In simpler terms, she's calling Apple Bloom inbred.
Growing the Beard: Captain Hook The Biker Gorilla is arguably one for Rainbow Dash Presents, though others may argue Cupcakes (the preceding episode) was where the beard started to grow.
For Mentally Advanced itself, Episode 3 (the Gilda episode) is where the series started to become funny, and Episode 7 ("Bridle Gossip") is the point where things really began to hum.
For the "Negative" episodes, the art quality took a huge leap between episode 4 and episode 5.
Pretty much everything Pony-related Greg and his team make ends up on EQD's front-page nowadays, including Captain Hook the Biker Gorilla, which was begrudgingly given its own post with a descriptor saying simply "You win." – apparently a number of Equestria Daily's users had also been complaining about the site's pro-Witchcraft bias.
Rarity is racist against non-Unicorns. Many fans believe her father, Hondo Flanks (Fan Nickname "Magnum") is an Earth Pony. Although Word of God has implied he is probably also a Unicorn, later confirmed in the episode "Inspiration Manifestation".
Jerkass Woobie: Twilight, after we find out exactly what Celestia did to her.
Les Yay: Pinkie Pie falls in love with Gilda's Jerkass tendencies, and she throws a party to try to tear her and Rainbow Dash apart.
In Rainbow Dash Presents: Haunting Nightmare, Pinkie is constantly coming on to Twilight, and even tries to drug her drink.
Pinkie: So, does it hurt when you run through Pinkie's dreams? Yes.
Finally confirmed in Episode 12:
Rarity: (regarding her breakup) "It's the way colts are, but we deal with what we're given." Pinkie: "Pinkie is lesbian."
They Changed It, Now It Sucks: Some people claimed this over the new theme song. Perhaps telling that Greg only used it twice before dropping the idea of a theme song completely.
The switch from traditional abridging to episode screenshots, done partly to speed up editing and partly to avoid copyright claims (the latter ultimately failed).
Later, and more pointedly, the switch from episode screenshots to hand drawn images and/or restarting the series from the beginning. To be fair, the first of those was done out of desperation brought on by ContentID necessitating taking down the videos; the alternative would have been ending the show entirely.
They Wasted a Perfectly Good Character: According to Word of God, Discord was Killed Off for Real by Celestia, long before he had a chance to appear in the series proper, partially to reinforce how confidant this version of Celestia is and partially, to avoid Hype Backlash, because of Greg's worries that he would not be able to live of to all the hype for his version of Discord. Instead, Discord has apparently been replaced by Breezen, a villain from Generation One.
What an Idiot: Fluttershy takes Celestia's sick pet phoenix without permission so that she can cure its illness with love and affection. An utterly horrified Twilight points out how this will not only incur the wrath of the tyrannical god-princess, but that said god-princess can (and does) provide better round-the-clock care for the bird than the pegasus could ever hope to achieve. Naturally, Fluttershy's efforts are disastrous, and Celestia punishes her for the crime.
The Woobie: Even when played for laughs, Fluttershy still manages to be this.
Aurora in Rainbow Dash Presents: Captain Hook the Biker Gorilla.