I don't know if this has ever been done before, but what's your favorite part of each episode? Here's mine.

(Note: As comments can get long you don't have to list "undecided" episodes, maybe only list most notable, or else post your own blog and link to it in comments)

Season 1:

  1. Friendship is Magic Part 1 - Applejack biting Rainbow Dash's tail for the first time
  2. Friendship is Magic Part 2 - The fight with Nightmare Moon
  3. The Ticket Master - When Rainbow Dash appears in the hole in the clouds like God on Monty Python
  4. Applebuck Season - "Kelp? I don't need kelp. I don't even like seaweed."
  5. Griffon the Brush-Off - The chase scene with Pinkie Pie and Rainbow Dash
  6. Boast Busters - Snips and Snails's reaction to finding out Trixie didn't vanquish an Ursa Major
  7. Dragonshy - Pinkie Pie and Rarity on tic tac toe
  8. Look Before You Sleep - Applejack saying "damn"
  9. Bridle Gossip - "Supernaturals. Natural remedies and cure-alls that are simply super."
  10. Swarm of the Century - Pinkie Pie playing the instruments and leading the Parasprites away. Well, that or her trombone scene
  11. Winter Wrap-Up - Hands down, when "Ditzy Doo" goes north to get the southern birds and went west last year
  12. Call of the Cutie - The unicorn popping the balloons whose cutie mark is a pin
  13. Fall Weather Friends - The entire Running of the Leaves
  14. Suited for Success - Rarity's song
  15. Feeling Pinkie Keen - When Pinkie's tail twitches and Celestia is what falls from the sky. Either that or Twilight turning into Rapidash
  16. Sonic Rainboom - Rarity's Icarus moment, and Rainbow Dash's Sonic Rainboom. Either that, or (yay)
  17. Stare Master - Fluttershy using The Stare on the cockatrice.
  18. The Show Stoppers - Hmmmm... I guess any scenes of Sweetie Belle singing
  19. A Dog and Pony Show - The whole "biting tails" chain with Spike, Applejack, Twilight, Rainbow Dash, Fluttershy, and Pinkie Pie
  20. Green Isn't Your Color - Twilight's random "Spike has a crush on Rarity!" And Pinkie appears in the mirror. (?)
  21. Over A Barrel - The salt bar. (either that or Scott McNeil doing the voice of Chief Thunderhooves)
  22. A Bird in the Hoof - Pinkie Pie eating the cupcake Celestia was about to eat, she doesn't react but Mrs. Cake bites her tail and pulls her away (which Celestia does seem to react to)
  23. The Cutie Mark Chronicles - Either Rainbow Dash's Sonic Rainboom or Pinkie Pie coming into direct contact with it styling her mane and tail
  24. Owl's Well that Ends Well - As dark as this sounds, when the green dragon tries to eat Spike. Cannibal. Either that or the punch being "spiked"
  25. Party of One - Again dark, but when Pinkie goes insane and has her own party and having some of new "new friends" call the other Mane 5 losers. (simply coz "losers" was muted out on Treehouse channel)
  26. The Best Night Ever - The Gala song

Season 2:

  1. The Return of Harmony Part 1 - Discord taking away Rainbow Dash's wings before he takes Fluttershy's wings and Twilight and Rarity's horns.
  2. The Return of Harmony Part 2 - Discord drinking the glass and throwing the drink away which explodes
  3. Lesson Zero - Fluttershy supposedly snapping the bear's neck
  4. Luna Eclipsed - Probably all Luna's scenes
  5. Sisterhooves Social - When Applejack and Rarity switch places
  6. The Cutie Pox - Kinda dark, but... "I'm gonna be as old as Granny Smith and still have a blank flank!"
  7. May the Best Pet Win - Either the race, or Opal hissing at Rainbow Dash
  8. The Mysterious Mare Do Well - When Mare Do Well's true identity is revealed
  9. Sweet and Elite - Rarity's song. That, or Fancy Pants
  10. Secret of My Excess - Spike confessing his love for Rarity
  11. Hearth's Warming Eve - The Windigos getting incinerated
  12. Family Appreciation Day - The "biting tails" chain of Apple Bloom, Scootaloo, and Sweetie Belle.
  13. Baby Cakes - The scene near the end reminiscent of Jack-Jack attack
  14. The Last Roundup - Derpy, hands down
  15. The Super Speedy Cider Squeezy 6000 - Flim and Flam getting run out of town
  16. Read It and Weep - The entire Daring Do book
  17. Hearts and Hooves Day - Undecided
  18. A Friend in Deed - The Smile Song
  19. Putting Your Hoof Down - Rarity biting Fluttershy's tail
  20. It's About Time - The whole paradox
  21. Dragon Quest - The whole scene with Fluttershy and Rainbow Dash at the beginning.
  22. Hurricane Fluttershy - Most of Fluttershy's scenes
  23. Ponyville Confidential - "I'll destroy her!"
  24. MMMystery on the Friendship Express - All of it.
  25. A Canterlot Wedding Part 1 - I guess the song "Big Brother Best Friend Forever"
  26. A Canterlot Wedding Part 2 - The entire fight with Chrysalis and the changelings, also Chrysalis's particularly sinister verse in This Day Aria

Season 3:

  1. The Crystal Empire Part 1 - The whole chase scene with Sombra
  2. The Crystal Empire Part 2 - King Sombra's death scene
  3. Too Many Pinkie Pies - When the one clone jumps to the ceiling, and Twilight destroys the one who looks up after her first
  4. One Bad Apple - Diamond Tiara and Silver Spoon falling in the mud
  5. Magic Duel - Twilight's second duel with Trixie
  6. Sleepless in Ponyville - Luna's scene
  7. Wonderbolts Academy - Spitfire making Rainbow Dash a leader
  8. Apple Family Reunion - When the pig dances with the rooster
  9. Spike at your Service - Either "I'll wear this mustache", or Rarity inside the cannon for no reason.
  10. Keep Calm and Flutter On - Discord's redemption
  11. Just for Sidekicks - Donut Joe's cameo
  12. Games Ponies Play - When Rainbow Dash mentions King Sombra
  13. Magical Mystery Cure - The songs

Equestria Girls - The fight with Demon Sunset Shimmer

Season 4:

  1. Princess Twilight Sparkle Part 1 - Pinkie's tail twitches, vine punches Rarity, Applejack kills vine
  2. Princess Twilight Sparkle Part 2 - Celestia vs. Nightmare Moon
  3. Castle Mane-ia - All the scenes where Rainbow Dash, Applejack, Rarity, and Fluttershy are going through the castle and falling victim to its traps
  4. Daring Don't - Rainbow Dash
  5. Flight to the Finish - The Cutie Mark Crusaders unaffected by Diamond Tiara and Silver Spoon's "blank flank" taunt
  6. Power Ponies - The fight with The Mane-iac
  7. Bats! - Either the song or the Bat Signals
  8. Rarity Takes Manehattan - Hmmm... How about the fact that we finally got another Rarity episode for the first time in a while? Otherwise, undecided
  9. Pinkie Apple Pie - Pinkie Pie taking the picture with her tail
  10. Rainbow Falls - Derpy's appearance
  11. Three's A Crowd - Either Discord's song or the fight with the graboid
  12. Pinkie Pride - The goof-off
  13. Simple Ways - Rarity hiding under Twilight's tail
  14. Filli Vanilli - The return of Poison Joke and Flutterguy
  15. Twilight Time - Undecided
  16. It Ain't Easy Being Breezies - Undecided
  17. Somepony to Watch Over Me - The chimera
  18. Maud Pie - Maud's obsession with rocks
  19. For Whom the Sweetie Belle Toils - Luna's appearances
  20. Leap of Faith - The Flim Flam brothers' song
  21. Testing, Testing, 1, 2, 3 - Rainbow Dash being adorable in that one scene
  22. Trade Ya - Applejack and Rarity (seeing how powerful their friendship has become since Look Before You Sleep)
  23. Inspiration Manifestation - Rarity "nom nom nom"
  24. Equestria Games - Appearance of all the princesses
  25. Twilight's Kingdom Part 1 - The princesses' song
  26. Twilight's Kingdom Part 2 - Twilight vs. Tirek hands down