Topic on Talk:Designated Hero
When I consider newer SMG4 videos, say, from early 2020 on or so, Meggy is actually quite nice, appropriately called the Morality Pet in TVTropes. The Fanon Wiki about SMG4 also paints her overall very positively. I would argue this to be Character Development though, just as Saiko changed from a villain in her first appearance to a jerkass and later to a mostly nice character. The Mario Mafia seems to be a rather exceptional sequel in that sense. Maybe the authors experimented a bit with Meggy and then concluded that they don't like this Knight Templar interpretation, making her nicer and more social in later sequels. (Meggy is still pretty new in The Mario Mafia.) There is even a later video where she's a police officer working with Mr. Monitor, and she opposes his knight-templarish pursue of justice, trying to argue with the transgressors instead of beating them up and torturing them.
It's probably not a coincidence that Meggy's appearance changes from Inkling to Human somewhere through her appearances. While early Meggy isn't really evil, safe from aforementioned exception, she is quite a Trigger Happy adrenaline junkie whose impulse control still has room for improvement. (Sounds a lot like she has Attention Deficit Ooh Shiny.) Human Meggy has grown more social and more level-headed, mirroring her change in appearance from Uncanny Valley to quite cute and adorable.
Apparently almost nobody calls her out for being a huge jerk in The Mario Mafia, because this is a rather singular event which can be seen as an Out of Character moment in an otherwise heroic figure. Also, by quantity she does not cause the biggest havoc - she kills one Koopaling, Steve kills the rest, and Mario lets his fellow Po die after Bowser injured him. You must watch the video carefully to see how she stands out by her seriousness and unstoppable determination to end the rivalry via Final Solution, while the rest follows a rather erratic course of action. Lastly, people are used to seeing Bowser and the Koopalings as the Bad Guys, and therefore some may lack the mental flexibility to look at the thing from another perspective. The video also does anything to obfuscate the picture, like by having them be the first ones to use guns (when Mario vandalizes Bowser's Clown car), or by Wendy pulling BFGs out of nowhere during her stand-off with Meggy (distracting from the fact that Meggy has just cornered her, forcing her to defend). See also Crosses the Line Twice.
Overall, Meggy in SMG4: The Mario Mafia is more a case of Adaptational Villainy that has been forgotten over time, and so gets no longer mentioned in Meggy's characterization. It's just jarring when you read about how warm and friendly she is, and then watch this video... THIS TROPE HERE kicks in with full force. (At least for me.) Mario, Steve and Toad aren't much better, but these are more often seen doing mischief in SMG4 than Meggy. And Bob... is actually quite himself, I think.
Oof. So much interpretation about an 11 min video that was created For the Lulz by two guys who probably didn't think about the plot points that deeply.
Still, I must admit that evil (or Knight Templar) Meggy is interesting. As I said I would enjoy a good fan-made sequel in typical SMG4 style... where the gang's plans go crashing down only to get resolved comically at the end.