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.
Rainbow Dash bristles, in one strip, at being told she could use 20% more breasts.
Pinkie Pie as well. In one strip, where Spike mentions she should call herself Flatie Pie, she reacts angrily by summoning Meteor to flatten him.
Adorkable: Derpy, in every comic she appears. A well-meaning Cute Clumsy Girl with serious Cloudcuckoolander issues. In one strip she finally realizes that focusing on an object allows her to see better. In another strip, she ends up destroying things that she meant to fix, or fixing things that she meant to destroy.
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.
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.
In the second fanbook, Applejack mocks Twilight's floppy horn, mentioning it shoulda been hard in the morning instead.
Celestia trolls Luna by asking her 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.
The comic parodies the series and its need to sell toys by having one strip be about all the Mane Six 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"
"Episode 0", an 8-page special in proper manga format, depicting the alternate debut of this series.
Celestia's Nightmare is a full page comic that in part parodies "Mega Milk".
A couple of one-shot pages focus on Twilight and Pinkie in the library.
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.
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.