Well, do you? (Note that characters spotlighted in Slice of Life and Amending Fences still count.)

Bulk Biceps has kind of graduated above "one-line background pony", but he's about the only one I can think of that's strong in the headcanons. :B Ponies who don't talk aren't that interesting.

7038957 Didn't stop a lot of the early background ponies from getting entire headcanons built around them for only one scene. Berry Punch became an alcoholic solely because of one scene where she drank out of a punch bowl at a party. And Lyra became what she was because of one scene of her sitting like a human when ponies didn't do that all the time.

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There were also a lot fewer background ponies then, because copy-paste crowd shots.

Your own answer is missing, Latecomer.

Hmmm. Let's see.

1) Lyra Heartstrings. Born in Ponyville. Played in the Canterlot Royal Orchestra. Befriended Octavia. Got bored and resigned. Moved back to Ponyville and fell in love with Bon Bon. Is maniacally obsessed with humanoids. (See: Storm King. (Younger) dragons. Diamond Dogs?)

2) Vinyl Scratch. Born in Canterlot. Visited the Royal Symphony Academy, dropped out after one year. Became an underground hit in the clubbing scene, but got quickly bored of Canterlot. Moved to Ponyville. Lower rent, lower food prices, lower everything. As long as it's not about her music, she's kinda messy-lazy. So she just made herself rarer, played fewer gigs. Somehow, that only made her more famous. Strange how things work. She met a very drunk and frustrated Octavia in Canterlot. Convinced her to move in with her in Ponyville after her family kicked her out. (How dare she be fed up with a hollow feeling lifestyle? How dare she resign from playing First Cello in the Royal Orchestra?) They lived together for a while before sparks started flying. Vinyl is a mute and suffers from albinism. Surprisingly perky lad, all things considered.

3) Doctor Hooves. He's The Doctor. No idea how he ended up here. I'm not even sure he knows. He might be searching for a way home.

4) Derpy. Does she even count as a background pony at this point? Anyway. She has a birth defect. Her eyes are a bit wonky. She only flies when absolutely necessary. That's why she lives in Ponyville. Laid back town, most mail can be delivered by walking. She has a daughter, Dinky. Nopony knows who the father is. She doesn't tell. Very chipper mare. Quite a flirt, too. She has lived with her disability her entire life, so there's little she hasn't heard already, insult-wise. What hurts her isn't the insult itself. It's the intention behind it. But she knows how to deal with bullies. Ignore them. And if they get funny ideas - kick them. She's a pegasus, after all. Ponies seem to forget at times that there's warrior spirit running in her blood. Oh and she actually has dream magic, which is very unusual. She's a lucid dreamer, has been her entire life. She's actually confused that this doesn't appear to be normal, and can't quite understand how other ponies don't dream like that. However, she can't exit her own dream without help. (Which would allow her to traverse the dreamscape and enter other dreamer's dreams.)

I think that's it for now.

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My brain blanks when questions are too broad... you'll see more of that in the 40s.

1) Lyra Heartstrings. Born in Ponyville. Played in the Canterlot Royal Orchestra. Befriended Octavia. Got bored and resigned. Moved back to Ponyville and fell in love with Bon Bon. Is maniacally obsessed with humanoids. (See: Storm King. (Younger) dragons. Diamond Dogs?)

Was there a part where she was part of Twilight's circle?

And interesting takes. Wonder if Luna might consider Derpy as an apprentice?

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My brain blanks when questions are too broad... you'll see more of that in the 40s.

Heh. I see. Well, looking forward to those then. I have no idea how I'll handle those.

Was there a part where she was part of Twilight's circle?

Yes. Brief period, basically a proto-friendship. But she was part of that first bunch.

And interesting takes. Wonder if Luna might consider Derpy as an apprentice?

In my version, Luna was absolutely flabbergasted. And she wasn't even the one to discover it. I have an OC that has dream magic. Now, he was a little bit reckless with its usage, which made Luna become aware of him. She insisted that he needed to be trained, as to not endanger others further than he already had. A nice bonus for her was the fact that he could help alleviate her burden. Back in the olden days, there were A LOT less ponies. (A lot less sentient creatures in general, since the dreamscape doesn't just contain dreaming ponies, but dreaming EVERYTHING. Griffons, dragons, changelings, every sentient creature capable of dreaming.) So she returns to a world a lot fuller than she knew it before. And her tasks have multiplied a lot. So many nightmares to deal with. Despite his interference, this idiot can be useful. (She's a bit... protective of her domain. It's an alicorn-thing. Cadance can unleash surprising fury when someone else meddles in her domain, too.) Anyway. So she takes this idiot under her wing, kind of. Sends him to Canterlot, Night Guard training. And after that, they are now... two ponies doing her job. Still way too few. And then he stumbles upon this revelation that Derpy doesn't actually know or understand her own cutie mark. (And thinks the CMCs obsession with them is a little creepy, hence she never tells them.) He figures it out and they introduce her to Luna. Now there's three of them. And they come to a realization: Nopony knows how cutie marks are distributed, exactly. With a world constantly growing in population, wouldn't it make sense for there to be more and more ponies capable of helping dreamers? So they turn to Twilight. Being the Princess of Books and Smarts and such. And she modifies a nifty little spell to search for dream magic. And there's singular little dots blinking all over Equestria. They are few, but they are there. And suddenly, Luna realizes that maybe, just maybe, she doesn't have to shoulder these duties alone anymore.