Say if you write a MLP fanfiction (or any fanfiction for that matter)... And you write, you post your story, and guess what?? You know you made a HUGE MISTAKE.

That huge mistake being that the facts JUST DON'T MATCH.

A moment when you get something related to the MLP universe completely wrong, and you've already published it...

I guess that's why people look stuff up first, to make 100% sure... I know i learned my lesson... but has anyone ever had a moment like that? Where you realize that what you write in your fic doesn't match with the MLP timeline? I'm sure fans would find it completely unacceptable.

People research the show for fics?

Well, I can't say this has ever happened to me. But, that being said, my story is only written from the vantage point of a post-season 2, pre-seaon 3. If it's a timeline issue you're talking about, then really, you're interpretation of the timeline is largely your own. Can't really tell since you haven't stated what exactly your mistake was.

I don't think I've published any mistakes like that yet. I have caught myself doing it before. The biggest piece of advice I have is....

Paper and pen!
The point is to plan out your chapters ahead of time. By summarizing what you envision, you can surprisingly catch mistakes before they become too extensive and allow you to build your frame first. From there you can start fleshing it out without getting lost in the little details. I have also turned my planning drafts into a kind of concordance, writing little notes to myself in future chapters that will build off of the previous ones.
To each is their own, but I have found this helpful.

589533 Has happened to me... I fixed it and allowed for some character development, but some people have said my fix was slightly clumsy.

Not yet.
So far the only story I've published is a slice of life/comedy that really could happen at any time after the Baby Cakes episode and the second one I'm working on takes place after the Changeling invasion, but since it has OCs none of the other events really have any baring on it.

However I have had muck-ups with in my own original fics where stuff didn't line up, like the character that aged 2 years in several weeks *derp face* I listed him as one age at one point early on, then later (several weeks in the stories time line) I said he was a different age, several ears older. At least I caught that when proofreading though.

589542
Ah, it's not about the timeline. It's the LOCATION.
When that doesn't add up when you're describing the place, a place that already exists... then well, that's where I had my mistake at.

I went and corrected it, but my mistake specifically, was when I mentioned the Wonderbolts Academy, I went to the FiM Wiki, and found out that the place looked different from what i described it as, so i had to hurry and change it.

589578

Oh, that isn't as bad as it could have been, and at least you were able to change it soon after.

589569 Been there, done that. It's worse when dealing with flashbacks because you have to make sure that if you mention an event from the show, you don't mention another saying that they have magically aged a few years. (After all, if Twilight Sparkle can't do age spells, no pony can.)

589584
Yeah, I usually try to be careful when it comes to location and timeline and all of that jazz. But for me, messing up the location is much easier than messing up with the timeline in my opinion.

With the timeline, I can always just do a double check through the episode summaries and things that happened. With Location, if i can't find specifics, it's a bit difficult, really, especially when I'm trying to get back into Fanfic writing.

The timeline can even be handwaved with a little disclaimer that diverts away from the original timeline.

Gah, I think i just rambled too much.

589533

Mine involves McDonalds.

You probably don't wanna know.

I said that only Celestia and Luna could raise the sun and moon, completely forgot about unicorns raising it before the princesses did. But I managed to fix it.

589533 This very nearly happened to me. There I was, writing my epic story about Celestia, when I needed to have Starswirl the Bearded meet his mentor, Clover the Clever...

The problem? Clover wasn't Starswirl's mentor, it was the other way around. I had completely forgotten that. I happened to watch Hearths Warming Eve right before I wrote that scene, and I tell you, I was practically blushing even though I was sitting by myself, just thinking of how embarassing that would have been...

It was a close call, but no one found out. Until now.

I've done that. In one story I wrote, I thought Sugercube Corner was the name of an intersection in Ponyville, and that the store Pinkie Pie worked in was simply located on it. Let it be known that there are no buildings on top of buildings in my head-cannon.

In your opinion, how bad is it to mess up accepted fanon names? Example, I think I called Inkie Blinkie, and Lotus Aloe in two different (still unpublished) stories, and I'm wondering how big a faux pas this is.
Yes, I screwed up in two different stories. Stop judging me.

600203

I hardly think it's that big a deal to mess up the names of any pony that's not in the show. There's a lot of fanon out there, after all, and not all of it is consistent. Although some, like Lyra, Bon Bon, and Derpy should probably be gotten right.

600203 Given that many fanon's have multiple names, it is not a large issue

The steroid pegasus with the tiny wings is variously called Horse Power, 'Roid Rage, and Snowflake

Twilight's father is either called Night Light or Orion.

As long as you are close, most people will forgive you.

607978 Is her mother Twilight Velvet or Twilight Star?

612653 Twilight Velvet mostly, but a few Stars along with a third name - Dazzle

Given that neither of them have had any dialogue yet, no one has really clamped down on their names. Just so long as you are clear about who it is meant to be, the final name generally doesn't matter as much.

Now a clearly fan defined secondary or background pony on the other hand - best get those right, down to the exact spelling.