As in, where the character's name and/or pronouns would be used? For instance,

Twilight Sparkle rummaged through her shelves, scowling.

"What's wrong, Twi?" Rainbow Dash asked.

The lavender unicorn snorted and rolled her eyes, making sure to turn her back so the cyan pegasus couldn't see said eyeroll. "Nothing, Dash," she hissed sarcastically.

I heard many times it's bad, but I've also heard that it can be good. Thoughts?

5516330
Just as long as it's not overdone. (Say: three times in ten small-medium paragraphs, or so.) I think it can be used wisely. The Example above seems to be a decent enough use, though.

5516330
I think there are cases where sometimes it can work; SUPER small doses for canon characters, especially if they're major ones who most readers should be familiar with. But if you're introducing an OC or obscure character, then it's not bad to use it early on, necessarily, just don't keep doing it once you've explained what they look like.

5516333 Alright, I can get behind that.
5516336 Hrm, duly noted.

5516330
Depends on how long the story is. On average, maybe once or twice in the story. It annoys me if done more than that if it's really noticeable but I learn not to care.

5516330 Use names and pronouns at all costs. Then sprinkle in some diversity if it begins to feel stale or when some clarification is needed. I'd say for your example it doesn't work. The cyan pegasus description is alright, but the 'lavender unicorn' bit doesn't work at all. Especially since it is in the same sentence as the Rainbow Dash description. Just keep their names, and if you do use a description, instead of a name or pronoun, try to keep it subtle. If a stallion and mare are by themselves, maybe just say 'the stallion' or 'the mare'. Or say, "the excitable party pony" for ponies like Pinkie Pie (I don't know if I would use that exact phrase in anything but a comedy or if Pinkie was really doing something... Pinkie-like). Make sure it fits the situation or context and try to keep it very sparse, or if it clarifies/adds something in the story.

In short, I agree with 5516345, 5516333, and 5516336.

5516377

5516330 Epitaphs can be used very sparingly, and with purpose, but I'd avoid 'lavender unicorn', in particular, simply because the first and only use is going to stick out like a sore thumb for anyone that's even remotely familiar with it. If I was to use any sort of visual descriptor at all, it would normally be for characters where there's actually some use in doing so, such as when you're introducing a character.

A recurring theme in a lot of writing conventions is minimizing distractions. If you are often calling a character 'the burly detective' instead of his name, then that's probably going to take the reader out of the story. The same is true of overusing 'said' and book-isms (he murmured, he yelled, and so on.) You'll often be given the advice to NEVER use 'he said/she said', bookims, and the like, but it's really a matter of style, and not everyone can make a completely minimalistic style work.

I tend to mix it up a bit. I'll try to avoid speech tags altogether as much as possible (without making the story confusing) and I'll use action tags wherever I feel appropriate, but I'll use 'said bookisms' very sparingly, as they're often considered to be among the most egregious of offenses. The same concept applies to names, pronouns, and epitaphs. If you're going to use the latter, the trick is to use it so sparingly, and in such a way that the reader doesn't actually notice. Put your chapter away for a week or two, and when you go back and read it, the epitaph jumps off the page at you, then it's probably time to get rid of it.

5516941 Hrm... alright. *nods and takes notes*

5516330
I wrote about this a while ago on my blog: http://www.fimfiction.net/blog/295088/style-blog-2-lavender-unicorn-syndrome

5516330 Well, the thing is is that we already know that Twilight is a lavender unicorn/alicorn. You don't need to tell us that; we already know this because we've seen the show countless times. Your only audience is from those who have watched the show, so explaining that Twilight has a lavender coat for others who haven't watched the show just wouldn't make sense, especially since you're writing on a website meant specifically for MLP.

5561842 True....

5516330 it's used when it's necessary to refer to a single character multiple times in a short span, but it's too soon after calling them by name to do it again. It gets really jarring when you see a character's name three times in two sentences, so things like "lavender Unicorn" are used as substitutes to break up the monotony.

I agree, it can be annoying if it's overused, but it's much better than hearing (as an example) Twilight's name repeated over and over again in two paragraphs.

5562323 True, but there are also pronouns (she, her, her's...).

5516330 I see it good if you're using it to describe a new character with a story you didn't name yet.

5562755 Alright.

5562738 yeah, but there are places where pronouns don't fit either.

For example:

"Twilight scratched her head in thought, the lavender Unicorn puzzling over yet another of Starswirl's incomplete spells."

"Lavender Unicorn" is just one thing that would fit here, "the scholar" or "the Mage" or anything like those would fit, but pronouns like "she" wouldn't fit unless you changed up the sentence. That is a viable option, but this is a place where 'L.U.S.' works and pronouns don't. It all depends on sentence structure really.

5563731 And how an author uses it. *nods*