EDIT: Upon going back over episodes a bit as well as seeing other people's thoughts, I'd like to bring up it's not just "Griffon the Brush-Off" that makes this characterization of Rainbow feel contradictory. "Scare Master", which happened before this episode, has Fluttershy clearly saying being scared is not for her and she wants no part in it and would like to avoid it. Hmmm interesting.
Revisiting this episode.
Still think it's bad. But I don't want to restate reasons that people have already specified in here, because honestly, I think reciting the same points over and over again was an issue with my comments I made a couple of years back.
I'll just sum it up by saying: I agree with the complaint that Rainbow's character regressed and that this retreads ground that she already learned a while ago and didn't need to be spelled out in its own episode, again, with a forced moral.
I'll instead bring up some other points that may have been lightly touched upon, or didn't mention much, or didn't mention at all, for the sake of provoking more thought:
1 - There's a very, very odd progression with the pranks in this episode, and I actually think it's something this episode did worse than "The Mysterious Mare-Do-Well". While the latter started out with small harmless boasting that progressed and escalated as the episode went on, this episode actually started with the worst prank first. Yeah, some of the other pranks were harmful to the ponies they were inflicted upon, but the first prank we see in the episode is undeniably the worst one given that it visibly brings Fluttershy to tears and gives her a panic attack and relating to the already mentioned 'regression' issue. Normally in an episode like this, the better structure is to have the pranks get worse and worse until the characters establish that they can't take it anymore and they have to do something about it. Not saying this can't work, but generally stuff like this is based upon escalation (and Rule of Threes, but that's a whole other discussion). And I definitely think it doesn't work in this particular episode, given...
2 - Some of the pranks are actually rather funny. The one that Rainbow does to Rarity in particular, I legitimately can't imagine anyone being offended by. No, seriously, I actually think that prank, if not objectively funny, is at least objectively clever and not all that obstructive. I know of no real world person who would be offended by that prank, and I legitimately can't think of any real person who would be offended by it, so the fact that Rarity is, is baffling to me. And if the reason is because of the outfit that Sweetie Belle was supposed to wear, Sweetie Belle herself didn't seem all that upset by it, and she's the one who's supposed to be wearing it... And there's another aspect to that...
3 - Since we're talking about "Griffon the Brush-Off" at all, I think it's not just Rainbow's attitude that was changed for this particular episode - all of the Mane 5 were different in their own way. Remember, Rainbow and Pinkie already pulled pranks on these gals before, pranks that were honestly less original and funny than some of the ones Rainbow pulled in this episode, and they laughed along with it. It's strange that suddenly now they're offended by it. You can say that they have changed and they just think it's juvenile now, but is that really a good change? Could you argue to me that it's a good thing that the characters have suddenly become allergic to the idea of fun?
4 - It's very evident that they were attempting to address the complaints that were in "The Mysterious Mare-Do-Well" with this episode given that they explicitly show Rainbow's friends talking to her twice in this episode. But here's the issue: I never wanted a retreated of MMDW in the first place. What I wanted, and what I think a vast majority of the people who complained about that episode wanted, was for them to learn from the mistakes of MMDW and use that to better other episodes. And this episode really does basically follow MMDW beat for beat and just change up what exactly they're complaining about in Rainbow's behavior, and what she's going too far with. Just replace "boasting" with "pranking", and it's the same premise in every other way.
And them doing something in MMDW and then better in this episode, I'm not about to give it a pass for. And the thing they did fix in this episode... They handled it pretty sloppily, and it rang pretty hollow for me. It is nice that it shows that Fluttershy has progressed to asserting that something is not funny and can stand up to her friends, but that's the only praise I can really give it.
5 - This one has been brought up before, unlike the others which either weren't or were lightly grazed over, but it bears repeating because it's actually the part of the episode that gets me the most. Showing up Rainbow and making her feel worthless like in MMDW is one thing. You could argue they didn't know Rainbow well enough by then to entirely understand that that kind of thing would put Rainbow at a low spot, and you could argue that they saw it as justified because they were still helping other ponies and it's not like they had any control over which 'hero' they favored (their boasting, though, was a bit excessive if their whole point was to illustrate that MMDW was supposed to represent being humble, like lmao, way to rub it in gals). But this is another entirely.
Others argued here that Rainbow could seriously hurt ponies in her pranks and they were awful because of that. While I agree the pranks were certainly risky, Rainbow carefully observed them and it was clear her intention was not to harm them (that scaring one doesn't count because that particular prank sticks out like a sore thumb, it doesn't feel like Rainbow would make such a prank and again, it doesn't fit in with the escalation narrative, and it's the one she undoubtedly acted the most insensitive about...i don't know, it's a weird one to me, but in that case maybe you could argue the harm caused by that would be a temporary scare and she didn't know it'd be panic attack inducing, even though Rainbow would have to be hit pretty hard by the idiot ball to believe that). The brick was probably the worst offender in that regard, but even then having bitten into hard things by accident the worst thing you're going to get is some jaw pain for a while. It's clear that to her if it was going to cause any harm it'd be like...pinching someone on St. Patrick's Day kind of harm, the kind you'd get over relatively quickly and sure it'd be annoying but nothing life-threatening. I'm not suggesting they're good pranks (because tbh they were really fucking stupid), but just that the damage that could be caused by them is relatively minor.
You know, relatively minor compared to believing that you fed an entire populace of ponies that you personally know and love cookies that turn them into zombified freaks like you spread a freaking plague over them.
My point is thus: the thing with MMDW may cause some trust issues at worst for a while, and it'd hurt Rainbow, but it's on the same level as inducing that panic attack in Fluttershy, that sort of thing. It's not something that would stick with her for very long... Despite what fanfic writers may say.
Tricking Rainbow into thinking for quite some time that she'd caused a plague on her friends that turned them into zombies is COMPLETELY different. That's an incredible trauma to induce on someone. It's like... On level with those "social experiment" pranks on YouTube. Like, damn, dude, that's way too far. And there's no, no way that they didn't think that would be traumatizing. Or, wouldn't, if they were real people.
I'm not angry at these characters for this, they're fictional characters, not worth getting angry at them about it. I'm...frustrated that the writers played that off as acceptable. I mean, I just don't know, some people would probably argue it was justified and weighted well, but I'd be in heavy, heavy disagreement with that.
Also, did anyone notice how Rainbow went to find and warn the remaining friends she thought she had...?
EDIT2: This review here has a lot of my issues, and why I actually think MMDW was better than 28PL.