I'm not Brazilian, so if you have a translator, I'd recommend using it.
DeviantArt, Fandom Wiki, and Tumblr (the last in which is the ULTIMATE hub for UTMV (Undertale AU fan content), which is a big deal) are the spaces where you can create an AU, though Reddit can also be used to pitch ideas.
The best option is to start with a form of digital art (Be it pixel art or digital art) and then do one of four things. There are other options in this community, but for what you're trying to make, there are four primary options:
The fanart route: Simply have a series of arts depicting the AU and its characters, an approach UNDERFELL originally took and was also taken by OUTERTALE.
The Web-comic route: The ol' reliable; A series of comics, be it an episodic series like Hand plates or Fellswap X or a bunch of comic shenanigans like with The Bad sanses or Min-play Underswap, though those are more akin to fanarts. Comics often have dialogue that needs to be written and multiple panels that show different perspectives and moments in the AU.
The Fangame route: It is nearly mandatory to do individual sprites (small artworks) and learn coding if you want to make a Brazillian UNDERTALE fangame. TS! Underswap, La Jupo Vania, The Thanatos duology and Undertale Yellow all fall under this umbrella. If you're going to do a fangame, I'd use gamejolt for this rather than Tumblr or Deviantart.
The Animation route: A full blown animation series of the AU, something only few big AUs have ever done, and for good reason... Xtale is the primary example of this path. If you manage to make a masterpiece of an AU animation series with this premise, I commend you. This is obviously where Youtube becomes the optimal website for sending this stuff.
If this is gonna be an aesthetic AU like Outertale, you can kinda just copy-paste UNDERTALE's lore and just change minor stuff to better fit the concept. If it's gonna be a full blown thing like TS! Underswap, a new (although maybe familiar) story is going to be optimal.
This design is probably one of my best works thus far where I was able to make a full on concept.
Here's a fun fact: Sterk's new motif is actually a song from Homestuck, specifically "Liquid Negrocity" or "Black", which are essentially the same song... one of motifs in "The world revolving" is referred to as the freedom motif, so in Sterk's case, the opening to LN/Black would be referred to as the "Midnight Crew motif", which will make sense in the timeline he's presented in for the new Determined Saga (Since the AU is gonna function more like Aftergore).
Credit is due, gotta thank Bagel-draws for his new design... I'm updating Sterk's lore and character traits to be more in line with canon UT, but there are still some major things that are staying:
He's still an apprentice by proxy for Gaster, but I'm changing the whole DT extractor thing because that project was Alphys' doing... the info on the experiment is mostly kept hidden, but it will drastically change Sterk's and Gaster's life to where the guy becomes insufferable.
Asgore still hates him, and vice versa. I mean, when your sworn enemy (human-kind in this kind) infiltrates parts of your working class and gets involved in the "death" of the man who did everyone a huge favor, it wouldn't be hard to throw shame on them (Gerson is still very neutral on the subject, given he understood Sterk's worry at the time).
The Deceit SOUL is a work of the darkness from Inferno/Hell/whatever ya' wanna call it... it's being updated so that it showcases a small amount of magic (think back to storyshift's reboot with Chara, given they have learned to use plant magic). Sterk isn't particularly a fighter, but rather a Proxy in multiple cases (As an apprentice in science for Gaster during his life, and as a member of a hivemind that's directly sent after certain people by Tam Tam after his death), but he does have a ton of tools to get the job done... just give him about 2-4 minutes to get everything situated.
He's still a scatter-brained knucklehead.
"Underlust... Ya' mean that [DATING ON TELEVISION] Pheo was working on a couple weeks ago? I think it's kind of hot. I mean, who could blame me, that [mechanical organism] sure is a [HOCHI MAMA]!"
"MnMs, what are those?"
That's actually a very complicated thing to do... a character that's powerful for no known reason isn't all that easy to flesh out... I mean, Betty was kind of both, but there is at least an explanation to her powers, hence she isn't OP for no reason... when I say poorly made, I don't just mean OP for no apparent reason or weaknesses, but it could also be something like character design or character traits. Maybe they are so generic to the undertale fandom to the point where it gets boring, or maybe their design is very incoherent with their character. Maybe they're just too perfect and don't have any flaws as a person whatsoever (which is exactly what a Mary sue is.)
That I can understand... really, I just wanted there to be categories that separated well written characters with ones that wouldn't be considered "well written" to the public eye. that way if someone's new to the Undertale fandom (especially a friend), It will be easier to show your friends the more fleshed out characters before moving onto crazy and unreasonably OP characters.
Well, I really just dislike frans, in my opinion, but yeah, I will admit that I was kind of an asshole by making this post.
"Hell yeah!- Uh... well, it actually depends."
"🕈︎☜︎☹︎☹︎ ✡︎☜︎✌︎☟︎📪︎ 👌︎🕆︎❄︎ 🕆︎☟︎📬︎📬︎📬︎ ✋︎ ☟︎✌︎☼︎👎︎☹︎✡︎ 🕆︎☠︎👎︎☜︎☼︎💧︎❄︎✌︎☠︎👎︎ ☜︎✞︎☜︎☼︎✡︎⚐︎☠︎☜︎ ☜︎☹︎💧︎☜︎🕯︎💧︎ 🕈︎✋︎☠︎☝︎ 👎︎✋︎☠︎☝︎💧︎📪︎ 💧︎⚐︎ ✋︎❄︎ ❄︎✌︎😐︎☜︎💧︎ ❄︎✋︎💣︎☜︎ ❄︎⚐︎ 👎︎☜︎👍︎✋︎🏱︎☟︎☜︎☼︎📬︎"
Question: "How in the [NINE CIRCLES OF HELL] did I get here!?"
Answer: " Oh... I see."
This guy gets a 3 or 4 in the scale of quality.
I wanted to have the guy give a Q&A just to get to know everyone on the fandom website. You (or your OC) can ask him any question (yes, any question), and you will get an answer from him... although, do expect some of his answers to be rather unexpected... this IS Dr. Raymond Sterk, after all.
The sprite looks even nicer, and definitely more accurate, but I still think there should be changes:
First off, the facial sprite would look more refined if it didn't use the glowing creepy face (or at least have the glowing eyes be much smaller than the eye sockets... think of sans's glowing eyes in undertale.)
Second of all, The handy helpers should come in 6, not 2. (and should be small enough to fit in his pockets.)
Lastly, you should invert the body colors (not the leg colors, just make the robe black, hand white, and buttons white.)
Otherwise, you overall did him rather well.
I would like a more refined version, especially without the two handy helpers... maybe do extra sprites for his different magic attacks (other than the ritual and electric tools, obviously)
As for other changes I'd make, would make since if his lab coat has buttons, and it would be cooler If he had both eyes has a blue glow yet remained stagnant. his left arm should be in his pockets while his other hand is held out, as If he's willing to make a deal with you. (think of a guy with some similarities to Spamton.)
Overall, it does look rather choppy and a bit like a 12 year old's drawing (no offense, it's just so weirdly shaped that it looks like someone glued a bunch of triangles and stuff together). and It would be rather simple If it weren't a GIF. of course, there's no need to rush yourself, and I would recommend taking a better look at shrubity's facial sprites.
Although I'm not gonna lie, It certainly does look cool.
I may not have a whole reference to him, but you can check out his page Here (which has his facial sprites and description), otherwise, I do recommend using this image as Inspiration.
I think It would be nice if more well written characters (EX: Dr. Sterk or Ulthrik Dreemurr) to be separated from characters who are "Cringe Inducing" (EX: Gill (Female sans who's also a potential sans ship child... and a potential Mary sue), Justice! sans (Frans character who's also semi-OP), and Infinitey code (Do I have to explain?)). It could really Inspire people to make more Interesting and unique OCs, and while it would seem rather rude to call someone's OC "dainted, dire, bad.", I find it rather necessary. How I see It would be for there to be two additional categories:
Dire - any Mediocre OCs who are
A mary sue
A frans character (or based on a similar ship)
Has little to no writing other than "They are ______" (must at least have some background, unless they're an NPC character or of similar grounds)
Is just a sans/Frisk/Undertale character Recolor with overpowered abilities
Everyone likes them "just because"
Is overpowered, Broken, and without flaws (especially the latter, and the former cannot be justified with "Just because".) (Ulthrik and Sterk can easily be excluded from this category since they both have flaws and have reasoning behind their abilities. Ulthrik is a boss monster, and Sterk Is a lich.)
Lucid - any well written OCs who
Have their own place in their own story, or just plain cool.
Can be an NPC, minor role, or even a major role (think of Itsy & bitsy, or red.)
Must not Harbor what makes a character "Dire".
Overall, I just wanna hear everyone's thoughts on this. I think It could really distinguish a Good character with one who's just "Outcode! Infinity! 404! Bill! Swap! female! sans".
Looks like cringe, no offense, but I'm not trying to lie here either.