Friendship is 4komagic: Same heroines, different bust-sizes!
Friendship is 4komagic is a Slice of Life webcomic, normally in Yonkoma format, by Taiwanese artist Han Jan, also known as Shepherd0821. The webcomic is obviously inspired by My Little Pony: Friendship Is Magic.Originally only available in taiwanese, it was picked up by a group of fans, collectively known as Retired Pyramid Head Scanlations, and translated into English, with the approval of the artist himself, which he himself later posts on his own deviantart and tumblr.The comics can be read on the scanlation group's tumblr, Sheperd's own tumblr, and Shepherd's deviantart gallery.The first fanbook can be read here.The second fanbook can be read here.
Breaking the Fourth Wall: Fluttershy's breasts tend to break them as well, although on a more literal sense, where they're shown to alter the shape of the 4koma panels.
Pinkie has no concept of a Fourth Wall, to the point that in one instance Pinkie Pie decides to learn Japanese, so she could voice herself after hearing that FiM was gonna be broadcast in Japan. She does.
British Royal Guards: Well, Equestrian Royal Guards, but the intention is the same, specially with Rainbow Dash trying to make them laugh by dancing like Twilight.
Catapult Nightmare: One strip where Celestia was dreaming that Luna is not only more popular than her (which is true even In-Universe), but also her breasts have grown larger, thus making it impossible for Celestia to send her back to the moon ever again.
Gamer Chick: We find out later that Luna loves gaming. And has developed some rage issues towards a couple of them.
Genki Girl: Pinkie, in most comics. Lampshaded on a strip where The Mask had no effect on her.
Green-Eyed Monster: Celestia towards Luna, because Luna is more popular/affable with the rest of the cast. Rarity towards Fluttershy, once, when Rarity was selected to be the Evil Queen whereas Fluttershy was selected to play Snow White.
Insane Troll Logic: Pinkie Pie. She claims Fluttershy is clearly Russian because she's big breasted, can be very assertive and fights bears.
Twilight also delves into this in one strip, using the existence of griffons as proof that interspecies unions should be possible.
Interspecies Romance: Lampshaded by Rarity in one strip, where she asks Twilight if its possible for ponies and dragons to crossbreed. Rainbow Dash and Fluttershy proceed to have some fun at her expense, much to her chagrin.
Lampshaded in another strip, with griffons.
Lampshaded Double Entendre: In the second fanbook, Applejack mocks Twilight's floppy horn, mentioning it shoulda been hard in the morning instead.
Celestia trolls Luna by asking Luna to describe what Celestia is doing. The scene explicitly makes it look like Celestial is giving someone a handjob, while in reality, she's pretending to be button-smashing at an arcade.
Malfunction Malady: Invoked on the third page of the second fanbook when we see what happens when Spike tries to send letters with the flu. It doesn't turn out THAT badly, but still.
Meganekko: Interestingly enough, not Rarity, but Rainbow Dash in a couple of strips. In one of them she says she wears them because if you're gonna be a writer, they're required as part of your apparel, and she wants to be one.
Merchandise-Driven: The comic parodies the series and its need to sell toys by having one strip be about all the mane 6 pitch products and Celestia collecting all the money from the sales.
Another strip has Pinkie Pie mention that ponies are born whenever Hasbro needs new merchandise, after Sweetie Belle asks that very same question.
Meta Guy: Pinkie Pie. Able to break into panels, reading others' speech bubbles, jump into real life situations and realizing ponies come from a toy company.
Moe: Invoked in page 2 of the second fanbook. When Rarity gets a wet mane (re. Sisterhooves Social), she turns out hot, but when Dashie tries it, she just gets a cold; Fluttershy sneezes later on, but comes out as cute as a result. Later, in the same fanbook, Dashie comes out as cute when she loses her glasses.
Physical God: Both Celestia and Luna. One strip have them playing a sort of air hockey by smashing celestial bodies against each other, mainly because they're bored. Celestial simply calls it "Playing Catch with my Sister"
Celestia's Nightmare is a full page comic that in part parodies "Mega Milk".
There's also Shepherd's levels-of-anthro series, which covers the Mane Six and several canon characters before dipping into fanmade OC ponies, from Fluffle Puff to lesser-known ones. The latest of these? PrincessUnikitty.
Split Personality: The Nightmare Moon side of Luna appears occasionally, but only when dealing with video games, like the infamous Error 37 that afflicted Diablo III in the early days of its release.
Pinkamena also appears on one strip, when Pinkie Pie is not allowed to enter a private party.
The Talk: A variation. Spike asks Twilight why its customary to give flowers to the one you like. Twilight replies that it might unconsciously do with flowers being the reproductive system of plants, so its a symbolical offering of your sexual organ to your partner as an indication you want to mate, at least from a biological standpoint. Spike chastises her for ruining the romantic mood...
Played with. Rarity is shocked when Sweetie Belle asks her where ponies come from. Pinkie Pie intercedes and explains that ponies are born whenever Hasbro needs new merchandise.