If your thing is My Little Pony then sites like Derpibooru are what you would be looking for. Booru type sites offer quite the assortment of settings and ways to post your artwork, along with various formats supported like mp4 and gif styles. Sites like these also offer settings to filter out any unwanted tag that you would not feel comfortable watching on your feed.
That being said, Derpibooru is one of the most well known sites offering My Little Pony works by fans, which vary from safe to watch all the way to NFSW territory and even some other more disturbing works like "grimdark," which is a word used in the site to cover gruesome works including gore and such unsavory themes. There are also other themes such as Involvement of underage characters in sexualized ways as well as other graphic depictions.
Fans should be wary of such themes if they are to create an account to to browse what the site offers, although I will state that you can pretty much find other nicer works by artists who submit wonderful art staying true to the theme of the cartoon shows. The site also offers a voting system where you can either up or down vote any submission displayed, as well as blocking it from view if you don't wish to see it again in future visits. Lastly the site also offers a favorites system to collect any submission you favor, as well as an anonymous setting used to both upload and comment on the site itself, keeping anonymity should you wish it.
It is also unfortunate that while it supports quite a number of rules and guidelines, some members and staff running the site often act in a horrid childlike manner to others, many using the anonymous setting to do so and taking advantage of it. Reports at times are ignored, at times scolding you for even bothering in doing such things and make it seem that if you are too sensible then perhaps you should join something else, which does not look pretty professional in the least.
The site also suffers from glitches like login issues, but other than that technical problems are quite minimal. If you plan on creating your own gallery to store My Little Pony related submissions, then this could be one of the options you would seek, although there are other places where you could be treated better.
Tl; dr Version: On this imageboard dedicated to My Little Pony, people fetishize rape, paedophilia, and necrophilia, relentlessly bully and harass their fellow members, there's an extremely popular original character that is a textbook Nazi (swastika cutie mark and all), and the rules are rarely enforced at all.
---------------------------
Derpibooru, the domain name of the revived Ponibooru, is an imageboard (or imagebooru) dedicated entirely to MLP: FiM fanart. Screenshots from the show, fanart, croosover fanart, and even the dreaded pony-pron is allowed there. It's a place with MILLIONS of pony images, where users can upvote or downvote and comment on the pictures, and different images are sorted with an extremely in-depth tagging system. Seriously, there's a tag for everything under the Sun; if there's something under the Sun that doesn't have a tag for it, you can just make it yourself. And, if there are certain pictures you don't like, you can filter out the tags those types of images use so you don't see them anymore.
Sounds like a pretty good idea on paper, right? Yeeaaahh... no.
I have an account there myself, have for going on four years, but I have never posted anything; not a comment, not a picture, nothing. I'm just there to look at the pictures, vote them up or down at times, and just... spy on everybody.
In those four years of lurking on Derpibooru, I can safely say that the website is little more than a cesspool for the MLP: FiM fandom's most toxic members. You know those fans you hear about that jack off to ponies? You know those fans you hear about that will tear apart someone over their opinion alone? You know those fans you hear about that will send death-threats to ya for disliking their favourite character?
Well, I've seen examples of the latter two in the comments sections of this website and the first one? Heh, all you have to do is put any character's name in the search bar with the mature content unfiltered. And God help you if you put the "toy" and "irl" tags into the search bar at the same time.
Some of the images on that website are so vile that I would get banned just for mentioning them here, but to sum them up as cleanly as I can: there are photographs of MLP: FiM merchandise covered in... ugh, I think you know what I'm getting at. And this sh** gets upvoted all the time! There are some characters in MLP: FiM that have the appearances, maturity, and personalities of 7-12 year old humans. These are called fillies and colts or, collectively, foals, and are children in every way that matters.
You wanna know something? There's pron of them too. Sometimes, it's having sex with other characters in the same age-group, sometimes they're sexing the adult characters from the show. I once saw someone call out an "artist" who draws this sort of art regularly, calling them a "paedophile". You wanna know what happened? About three people, on the side of the "foalcon artist", didn't even try to defend their "right" to draw it; they just told him to filter it and quit ruining everyone's fetishes.
And I think this is a good time to talk about the filtering system. The UI of the Filters page is so overcomplicated that I cannot, for the life of me, wrap my head around it, so anytime I'm browsing the art, I just have to downvote and move on with my life, unable to figure out how to filter it.
Anyway, back on topic. I've seen people commenting that their fetish is rape. I've seen people drawing pron of a character that is canonically LESS THAN A MONTH OLD. I've seen some absolutely stunning pictures of the canon characters and scenery from the show, such as an amazingly detailed picture of Canterlot (an in-show city situated on the side of a mountain). It has 366 upvotes and 270 favourites.
I looked up a "foalcon" picture on the site for comparison of votes; foalcon is the tag the site uses in an attempt to glorify paedophilia (they even define the tag as "for images of underage characters in a sexual context; human/anthro underage porn is not allowed."). You wanna know how many upvotes and favourites one of those foalcon pictures had? 626 and 463, respectively.
The fact that the amount of upvotes and faves is anywhere CLOSE to the amount on that scenery image is just appalling!
People there fetishize and glorify subjects like rape and necrophilia, abuse, and paedophilia by putting them under a different name and pretending they're different (yes, paedophilia and foalcon are two different tags; none of the images under the former are actually paedophiliac). You might say that they're cartoon horses, and that doesn't count as paedophilia, but tell me this: if these people can jack off to sexualized fictional children, then who's to say they wouldn't do the same with a real child? The same goes for the rape and necrophilia cases; you say you fetishize rape, you draw pictures of characters violently raping a dead body, how can we know you wouldn't rape a human being because "you get off to it"? How do we know you don't fantasize about raping a person to the point of death?
*sigh* I'm sorry. I needed to get that off of my chest because like Hell am I going to comment that on the website. I've seen other people try, it would be a waste of my time.
To sum up the rest of the website, people in the comments section start warring over the littlest of things and will. Not. Stop. Seriously, some arguments go on for pages and pages... The tagging system is used to harass and bully the artists of some pictures. For example, a mediocre image will get the tag "1000 hours in ms paint", if you make an opinionated picture or mention your opinion in the description or comments, you get called a "duck". "OP is a duck", "duckery in the description", "duckery in the comments", stuff like that when, half the time, it's nothing more than someone bringing up their genuine opinion on a subject.
There are user-specific tags, some which are complimenting, others of which are insulting. The most downvoted image on the entire website is, amidst a sea of the aforementioned things, a picture of the Mane Six (the six main characters of the show) fawning over Justin Beiber. With a grand total of 1,599 downvotes. You just cannot make this stuff up, y'know? And, if you're wondering, the most upvoted image is a gif of a pony character shaking her exposed (and unnecessarily detailed) clitoris at the "camera", and I couldn't go through one page of the comments section without feeling nauseous.
To sum it all up, Derpibooru is the home of the most toxic and troublesome slice of the fandom. Yes, people can have their fetishes, but when those fetishes glorify absolutely unforgivable crimes and subjects that have traumatized and killed real people, then it's going. Too. Far. Fetishize it all you want, but keep it to yourself.
If you have any decency or sanity at all whatsoever, then stay far, FAR away from Derpibooru. Trust me, it's for your own good. If you find those subjects that I mentioned up there totally fine and justifiable, then please leave and never ever come back into my life again. Thank you, and that will be all.