Since the very beginning, this show has taken the base quine model and dressed it in just about everything. With one character specializing in the "Art of the Dress", and entire episodes dedicated to decking out equines in holiday themed costumes, that is pretty much inevitable.
#10 - The Hearth's Warming Eve Costumes
From Chancellor Puddinghead with her ridiculous hat, to the adorable battle armor Fluttershy is decked out in, the Hearth's Warming Eve costumes were an excellent look at oldschool Equestria, and some of the more interesting designs in a show plagued by every flavor of dress imaginable.
I still can't decide on my favorite one. I think I'm honestly leaning toward Rarity. Her color scheme just works so well with that royalty getup.
#9 - Sunshine Smiles and Moonlight Raven's Sun and Moon Dresses
This was originally going to just be Moonlight, but Sunshine wouldn't stop jumping on my keyboard, so we just went with both. Really though, Moonlight's design looks like it would fit perfectly on Luna. I wouldn't complain at all if a future Gala episode had the Princess of the Night decked out in that thing.
Sunshine's dress fits her well. These two really are the perfect mini, non alicorn versions of the princesses.
#8 - Everything Rarity Wears in "Rarity Investigates"
I found it funny that the image above was actually tagged suggestive on Derpibooru. Can you do that to official stuff? These ponies seem to be doing that on their own a lot lately.
Rarity absolutely rocked it with her Noir lineup from "Rarity Investigates". I almost want to see an entire side series dedicated to her solving crimes, just to see her bust that thing out more often. Why don't we have a pony side series yet? Is EG really all we will ever get?
#7 - Cheerleader Ponies
Something about four legged creatures using pompoms is cute. Or maybe it's just ponies being ponies that does that. Regardless, these two look great in their cheerleader ensembles. Even Twilight Sparkle gets in on the action at one point. I don't think she can come close to the girls up above though.
#6 - Commander Easyglider
Deciding on a single outfit from the Wonderbolts history lesson is hard, but how can we resist the TOP GUN reference? I hear they fine you $5 if you reference the movie at the real Top Gun flight school. You have probably heard that too, considering it is literally re-posted every other day on Reddit, and from there everywhere else.
#5 - Applejack's Lion Costume
Take a pony, turn her into a cat. I've already been over why that works. The internet can't handle a concept like this. We have spent YEARS being conditioned to love it. Even if this isn't your favorite Nightmare Night costume, somewhere, deep down, you are loving it. No one is stronger than the internet brainwashing machine.
#4 - Daring Do
Regardless on where you fall in terms of her being a real character and not just a self insert of Rainbow Dash into her favorite adventure novels, Daring Do had one of the coolest outfits we've seen in a while. I actually ran out and watched Indiana Jones thanks to her. I had only ever seen the 2nd one.
#3 - Derpy's Halloween Costumes
Nopony celebrates Halloween better than Derpy! She gets the reality of the holiday. Everyone else speeds off and buys these ridiculously overpriced pre-made costumes, while she sits back, gets all the laughs, and becomes the life of the party by grabbing leftover paper around her house to fashion novelty stuff. I know I'm not the only one with a pile of toilet paper rolls overflowing out of the trash can under the bathroom sink. Look at that ingenuity at finding a use for them. Derpy is secretly a genius.
#2 - Princess Big Mac
What once was a joke by Pixelkitties, is now an actual canon thing Big Mac dreams about. Considering how at-home he was decked out as Orchard Blossom, I'm actually not that surprised.
just look at how regal that is though. Doesn't it make you hope Cadance and Shining Armor pop a colt out?
#1 - Fluttershy's Dangerous Mission Outfit
Everyone thinks Magic Duel is my favorite episode just because Trixie is the star in it. They are all completely correct. Trixie is AWESOME. But, just in case you don't agree with that, Fluttershy here pulled off the ULTIMATE PONY COMBO. For years leading up to this moment, ponies were being dressed in socks and sweaters in fanon at an almost scary rate. Butterqueiet here made it canon, and just in case that wasn't enough, she added bunny ears and goggles. Can we just hand her all the prizes?
HONORABLE MENTIONS
Big Mac as Orchard Blossom
Did he make that dress himself? Is Big Mac hiding a secret dress making talent out of fear that Rarity will feel intimidated? Or did he steal a leftover dress from Granny Smith's old days, when she was 2 feet taller and an extra 100 pounds? Big Mac gets an A+ for effort regardless of how he acquired it. Lookin' good stud.
At least that's what the puppet guy seems to think.
Bulk Biceps is a Pretty Pony
So pretty~
R.I.P. Bob Ross Discord
And he totally completed it by turning Twilight into a bat pony. That is the best part, because I said so.
Coco Pommel
How do you make a tiny hair thing and a tie work as an entire outfit? Put them on Coco Pommel. Look at how cute she is. Cuteee.
The Great and Powerful Trixie's Great and Powerful Hat and Cape that Are Totally Passed Down By Her Mother Who Died in a Tragic Accident Leaving Trixie To Fend For Herself Against A Cruel, Cruel World of Ponies That Don't Appreciate How Far She Has Come Despite So Much Adversity
Poor Trixie. You are all monsters. At least I have been there for her since day one.
Feel free to toss your favorites in the comments! I know we didn't get all of them. Trixie will make up for it though.