Did Rainbow Dash pull a terrifying prank on Fluttershy because she forgot how much Fluttershy hates being scared? Or did she genuinely believe Fluttershy grew enough after over five-and-a-half seasons of Character Development to handle it? Or did she just not care because she thinks Fluttershy's timidity and fear takes the fun out of events like Nightmare Night?
Some interpreted Rainbow's behavior as her being stressed out from Wonderbolts training (where such mischief wouldn't fly very well) and blowing off steam.
The townsponies have gotten some flack for enjoying the zombie apocalypse prank a little too much despite Rainbow's fear, basically making them guilty of the same thing as Rainbow. Granted, they're doing this to the pony that's been bothering them nonstop with her pranks; they might not have gone so over-the-top with any other victim, but can they really be faulted for finding some catharsis in pranking the prankster?
Author's Saving Throw: Many were worried this would be a retread of "The Mysterious Mare Do Well", the mixed message of which split fans down the middle on its questionable Aesop. This time, the writers made sure to emphasize why Dash's friends (and the town for that matter) were teaching her a lesson. They even made a genuine attempt to try talking to her about the problem and when she didn't listen, asked Pinkie to kindly tell Dash to quit it. They only went through with their zombie prank when Dash refused to relent. Not to mention the episode does a pretty chilling, but entertaining zombie parody.
Is this episode a vast improvement over "The Mysterious Mare Do Well" that addresses and fixes/avoids the problems of the former? Or is it just as bad as that episode, if not worse? It doesn't help that just like that episode and several other less popular ones, it's the writer's first script for the show (though at least the story concept is from Meghan McCarthy).
The problem ultimately lies with the handling of Rainbow Dash's character. While those who liked the episode liked that it rectified the handling of the supporting cast in MMDW (namely by avoiding the Disproportionate Retribution aspect through them only resorting to the elaborate comeuppance after repeated pleading with Dash fails), its detractors didn't like that it came at the cost of Dash holding the Jerkass Ball even more persistently than said episode, especially since her jerkish behavior had been toned down since Season 2. As a result, many feel this episode would have worked much better as a Season 1/2 episode instead, or is merely a demonstration of what MMDW should have been too little too late.
Then there's the whole "zombie" aspect of the revenge prank. Along with it being way too predictable and it being very similar to MMDW in terms of hypocrisy, some fans felt that it provided a Family-Unfriendly Aesop about the best way to get someone to stop doing pranks is to do another prank that could have ended up going horribly wrong. Others find it more justifiable since, as stated above, Rainbow Dash was no better and was insisting on continuing to prank the town even when she was talked to.
There's been lots and lots of fanmade works about zombie ponies since Season 1 with Story of the Blanks being one of the oldest and most prominent examples. Now after 6 years, there's finally an episode that explores the surface of the concept.
The first issue of the comic book even did a somewhat zombie pony story. Granted they were Changelings in that case, but still.
This episode was co-written by F. M. De Marco, who previously worked on Littlest Pet Shop (2012) . Ordinarily, it'd be a writer from this series going on to write for LPS, not the other way around, which is funny in an ironic way.
It's the Same, Now It Sucks!: The most common complaint about this episode is how similar it is to the earlier episode "The Mysterious Mare Do Well", despite her friends trying to talk to Dash about the problem this time. Aside from that one difference, it is basically the exact same plot, which didn't sit well with some folks.
Misblamed: Newcomer writer F. M. De Marco has gotten quite a bit of flak for the characterization, particularly Rainbow Dash, on account of the episode seemingly ignoring their Character Development beyond Season 2. However, this overlooks the fact that series veteran Meghan McCarthy came up with the general story; De Marco simply adapted the idea for the screenplay.
Fans have been hyped for zombie ponies as early as "Bridle Gossip", but were sorely let down by the fact that their appearance was all part of a prank. That is, assuming they didn't know already.
Heck, Pinkie's dilemma between pulling a town-scale prank with Dash and her own ethical views on pranking could've gotten its own episode.
The very concept of zombie ponies, prank or not, is considered to be a really cool idea by fans. Its too bad it was wasted on a recycled plot of a very unpopular episode.
Visual Effects of Awesome: The worm's-eye shot◊ of a zombified Pinkie Pie emerging from the cupboard features what may be one of the most sophisticated lighting effects the show has used, which lends greatly to the legitimate creepiness of the scene.