At least these are mine. What are yours?
Warning: contains spoilers
Honorable mention goes to:
- The ending of Fall Weather Friends (Twilight beats Rainbow Dash and Applejack after they made fun of her, they apologize to each other for being poor sports, then Princess Celestia unexpectedly appears)
- Rainbow Dash's Sonic Rainboom
- Rarity driving the Diamond Dogs nuts with her whining, to the point of them paying the Mane 6 all their gems just to take her away from them
- Amending Fences
- Testing Testing 1 2 3
- Castle Sweet Castle
- Queen Chrysalis - Unexpected villain episode, first Knight of Cerebus, first truly epic battle, and her whole defeat by the power of love
- Twilight pretending to do all those magic tricks to get Trixie to remove the Alicorn Amulet
- Discord's redemption
- Gilda's redemption
5: Twilight becoming an Alicorn
Magical Mystery Cure was a major turning point for the series. Twilight Sparkle becomes an alicorn, and a princess, and it kinda felt like the end of the series. Also, we can call her "Twilight Princess" now (like the Zelda game) and Rarity has her only shining moment of Season 3 by being the first to refer to the princesses' race as "alicorn" (Alicorn Amulet doesn't count).
Of course this generated rage, but that died down after Season 4 began and it became clear she's still the same Twilight we know and love.
4: The Dazzlings' defeat
Of all villains, the Dazzlings came the closest to winning, even when compared with King Sombra and Lord Tirek. They put everypony under their spell except the Rainbooms, Twilight, Sunset Shimmer, Spike, and Vinyl Scratch, Twilight couldn't find a counterspell, and the Humane 5 were arguing amongst themselves.
Then Sunset Shimmer, who drove the Humane 5 apart in the first film, does the exact opposite this time and gets them back together, after which Twilight figures out how to defeat the Dazzlings. Even so, the Rainbooms nearly lose the intense final battle, but for the second time Sunset Shimmer comes to the rescue and together they defeat the Dazzlings and take away their power.
3: King Sombra's death
I know plenty of you will disagree with me on this, on more than one level, but it still stands. Aside from it being spectacular and him being the most evil villain of the series, I felt the show needed at least one official villain death (Chrysalis doesn't count as official for reasons I don't need to get into again) to show that it isn't afraid to atleast kill off a villain, that it doesn't think itself as too much of a "kid show" that it can't do that. G1 killed Tirek and Lavan, and Disney movies used to do it all the time. I like a family-friendly show that's willing to do that coz it shows it has some level of "hardcore" (besides, I know most people prefer their shows to be more violent and dark than that, as evidenced by the popularity of the Dark Knight trilogy).
So what if the comics are set in a parallel universe where ghosts are canon and Radiant Hope revives him? (on that note I wouldn't mind if that Sombra was reformed somehow)
2: Twilight vs. Tirek
Where do I begin? First, Tirek himself. They finally rebooted the first ever G1 villain, who was by far the most evil and menacing. While G4 Tirek was slightly less menacing than his G1 counterpart and didn't die (or did he? Tartarus is where he would have ended up anyway if he did...) he makes up for it with a more epic and intense battle. Twilight vs. Tirek was Dragonball Z quality and I think the fight sequence could convince any skeptic of the show's popularity.
And of course there's the fact that it finalizes Discord's redemption and concludes the season-long Keys of Friendship arc, with Discord giving Twilight the final key to the mystery box where they get Rainbow Power. Tirek is all-powerful but with Rainbow Power the Mane 6 are completely unaffected by his attack and blast him back to hell where he belongs.
1: The Cutie Mark Crusaders getting their cutie marks
Crusaders of the Lost Mark started out as a regular episode: Cutie Mark Crusaders are looking for their cutie marks, and they have to deal with Diamond Tiara again. But about halfway through it turns into a redemption episode for Diamond Tiara, who antagonized the CMC before they even officially became the CMC. I'm sure Diamond Tiara's redemption was the most any of us expected of this episode, but then, on the anniversary of the day this show began, after five seasons and 109 episodes (or 98 if you start at Call of the Cutie), the CMC finally get their cutie marks!
Unlike Alicorn Twilight, this wasn't revealed ahead of time and came completely unexpected, and almost no one is raging over it, instead declaring this to be the best episode in the series. And this doesn't end their story right here, it opens up new possibilities just like Discord's redemption, seeing what their cutie marks are for.
And on a side note, as others have noted, they "accidentally" released the episode Scare Master, which comes after this episode, ahead of time. The Cutie Mark Crusaders are featured in this episode so at this point they have their cutie marks. Fortunately, spoilers on a Snape-Kills-Dumbledore scale were averted because they are wearing costumes for Nightmare Night, so their cutie marks cannot be seen and we all assumed they are still blank flanks. (some wonder if this was intentional)
This was probably the longest-awaited event in a TV series since a certain episode of The Mentalist, and possibly revived the positive energy the show once gave me