A Very Minty Hearth's Warming better be next year's Christmas-themed episode.

And speaking of Marble & Big Mac... less than two minutes into a holiday special and they just break Marble's heart like that?  Not cool.  I don't even ship them (nor anypony else), but that seemed... unnecessarily cruel.  Sure, he's dating Sugar Belle now, but maybe just leave it at 'turns out we're really related after all' and let them laugh about it instead (and yeah, it's such a distant relation it wouldn't matter anyway, but still, this is a show for kids) or just ignore it entirely.  Real life may not work that way, but this is MLP.  I guess she got over it pretty quickly though since she seemed fine in the next scene (mood whiplash much?).

My thoughts, for what they're worth...

I understand why they made a pony the villain this season.  The whole point of the student six is to show that creatures other than ponies can be friends.  What better way for Chancellor Neighsay to grasp that than to be shown a nasty pony while simultaneously being rescued by a dragon, griffin, hippogriff, changeling, and yak?

Unfortunately, that means as much as I want Cozy to be revealed as Chrysalis in disguise, I don't see it happening.  It would entirely defeat the purpose of the rather lackluster eighth season.

Considering that Tartarus is the underworld in Greek mythology, it seems very wrong to punish Cozy Glow (and as noted, the 'monsters') by sending her there.  She's a bad pony.  A bad, bad pony, but this is excessive punishment, especially if it turns out she's just a filly.  The thought she could be an adult mare that looks like a filly entered my mind as well.  I hope that turns out to be the case.  Because otherwise, the only explanation is Princess Celestia is up for reelection and her opponent has accused her of being soft on crime for letting anypony who apologizes off the hook...

Seriously, Celestia.  She's quite likely a filly.  This is exceptionally harsh when we've seen a pony cause significantly more harm to ponies and property alike (Trixie in Magic Duel), offer a token (not to mention, insincere) apology, and is then allowed to run off without even a slap on the wrist.  After her defeat nopony tries to lock her up, and she only comes up to apologize to Twilight later.  Her first appearance shows her to be arrogant and selfish (though not truly a villain).  She takes that plunge willingly via purchase of the alicorn amulet, which she uses purely for 'revenge' on a pony for the unforgivable sin of showing her up and saving the town when she herself couldn't.  But there were no repercussions for her (of course, she's a fan favorite... can't tick off the fanbase, right?).  Nobody likes Cozy Glow, so its okay (and yes, the rook on her flank is something I took note to right away - it hints that she's more than she appears, and that there's a game being played, and I truly love subtle clues like that).

As for jumping the shark, this is the first show I've felt jumped the shark multiple times.  Twilight's ascension was the first.  Out of left field, and completely threw off the dynamics of the show.  Then that was immediately followed by Equestria Girls which took the show even lower.  I suppose we can take this as a combined jump (ooooh, like jumping a whole row of sharks!).  The show has been tolerable the past few seasons (instead of episodes that invoked a strong positive or negative reaction like the first few seasons, I find the last few seasons have trended towards mediocrity with very few highs and lows, just bland middle-of-the-road episodes), but they've needed to continue to bring in new supporting cast members to have somepony learn the ever-more-heavy-handed lessons.  Was the second shark jump the 'magic castle tree' or 'school of friendship'?  That's what I'm not positive of.  It's either jumped the shark twice or thrice in my opinion.

All of which comes down to the show trying to continue to outdo itself.  From an 'epic' standpoint, it's hard to beat Twilight wielding the power of four alicorns in a one-on-one battle with a monstrous centaur, so they've got to do something to keep the audience interested.