Alright, now bear with me. What if, just WHAT IF Sombra is part of reason why Luna went all Nightmare Moon. And Luna was the one that actually enslaved the Crystal ponies, perhaps alongside Sombra, and hid the Crystal Heart. And that's why Celestia knew where to find the Crystal Heart. And Celestia had to go to war with the Crystal ponies to stop Luna. And that's why Celestia and Luna couldn't go to the Crystal Empire and had to send Twilight instead.

And WHAT IF Cadence was the one keeping Sombra locked away. And when Luna found out that Chrysalis had imprisoned Cadence, she went off to check for Sombra's return thinking that Celestia could handle Chrysalis. And that's why she was MIA for that fight and had no idea what went on when she returned.

And WHAT IF Celestia knew that Sombra had been freed after that and was trying to get his empire back. And she had part of her royal guard watching for the Crystal Empire's return for that reason. And "IT has returned" wasn't a weird, intentionally ominous line.

And WHAT IF that's all I've got. What then?!

569570
That's actually a pretty solid story you got there. Answers some questions from the end of season 2 and beginning of season 3. Would there be a romance between Sombra and Luna?

569755
I'd say no because I imagine Sombra swooping in to goad an already-doubting Luna. I can't see Sombra being "nice" in that encounter (or any, really), and I can't see Luna ever falling for Sombra after that.

If you haven't read Night's Favoured Child, I recommend not clicking the link below. It's possibly a spoiler for a very good story, but I think it accurately describes how that relationship would turn out.
http://pastebin.com/vvBb92vg

569869
Hmm, good point. So would Sombra have a backstory of any kind, or will he be a villain with no past?

570058
Maybe he somehow gained power under Discord's rule and is trying to bring him back, but he first needs the statue. This seems flexible enough that it doesn't need to be thoroughly explained to be usable, and it's possible to go deeper into this if needed.

I'm leaning away from the "Sombra is a spirit" idea because he seems to have died with that final magic heart blast of crystaliness. From the dealings with Discord, I get the feeling that spirits can't die.

I don't think a grudge against the Crystal Empire is necessary, but it may help. For example, if Sombra was informally overthrown in favor of Cadence, Luna might be able to relate to him through that.

EDIT: Maybe after being de facto overthrown by Cadence, he felt that his additions to the Crystal Empire were underappreciated and decided to take revenge on the crystal ponies and annex Equestria. I'm trying to make this similar to the idea that Nightmare Moon wanted to overthrow Celestia and create an eternal night because she felt underappreciated.

Five days later I realize that I hugely under-explained myself in the last post. I was thinking that Sombra was the original king of the Crystal Empire and that it really was an empire. Sombra had worked to expand it, and (out of the sky!) Cadence had suddenly gained popularity and loyalty, eventually moreso than Sombra. Sombra gets jealous and spiteful and decides to annex Equestria to show that he is Best King (in terms of bringing power to his empire). Knowing that he can't fight both Celestia and Luna, he persuades Luna to join him (the whole Nightmare Moon thing), and it goes on with the story described in that first post.

Just a backstory for Sombra, whether or not it's in the actual story.

Anyways, I had another idea. A less developed one. The overall goal is to describe why Twilight and Spike have the relationship that they do by walking through important memories of Spike's life (before Ponyville), from Twilight's perspective. I think it makes sense to do this from Twilight's perspective because we know nothing about Spike's personality in that time period. "Important memories" could be things like Spike's first time helping out Twilight, a particularly stressful study session, his first time meeting Moondancer, etc.

Random idea I got while lying awake for a few hours in the middle of the night (so it probably sucks^^). Anyway, here's the deal:
It's sortof canon that Pinkie Pie and Rainbow Dash prank peopleponies together, but what if they had some kind of competition between them as well? Like, a neverending game of dares between the two? Of course, Pinkie always manages somehow, being able to defy physics and all. Then one day Pinkie challenges RD to prank a certain somepony (maybe, while high on one of the spacecakes Pinkie made, RD blurted out she had a small crush on that somepony or idk). RD never turns down a challenge, as that would be the same as losing.
But halfway through the prank, things start to go wrong (use your imagination), and by the end, she either has to accept that things went too far and she lost, or it turns out the crush was mutual and she doesn't care that she lost a dare anymore. Maybe even make that a letter to Celestia.
Maybe Pinkie dared her to prank the electrician pony (yeah things start getting random now, beware), so she spent a lot of time putting a dummy lightswitch somewhere in her house (so she can call the electrician and say it's broken. Also it's difficult to use a screwdriver if you can't use magic). If the electrician isn't a pegasus, she would have to move her cloudhouse closer to the earth as well (or cloudwalking spells). Now the electrician is smart, and realizes he's being fooled in like a minute. He (or she) would bill RD a quite large amount of bits for the 'work' he had to do, and that's when RD realizes things went too far. Even if she has that many bits, she needs them to buy things at the market etc (like food or rainbow dye). In other words she's in trouble (or, she could pay by 'other means').

I really don't know why I get such ideas, and it can really go into any direction at the moment (as in, it could become a Romance, a Slice-of-Life, or just plain Random etc). I don't know whether I'm actually going to write this yet, but I like the idea of PP and RD having this internal prank/dare-competition.

Edit Jan 15: wow that sure was random. But I have to say, probably because I've written this out here, I did get another, much better idea yesterday, which I'm now sometimes working on.

589144
I'm not really one to read fics about Spike, but the idea is actually quite good I think. It might also give freedom to develop some of the background ponies a little?

Oooooh... a story where Fluttershy teaches Discord te true meaning of Christmas Hearths Warming Eve.

I had an idea for a (possible) comedy that involves the changelings kidnapping twilight (or maybe cadence), and to fool her they construct an elaborate and detailed recreation of ponyville and canterlot (or in cadence's case, the crystal empire), using changelings and plywood. And paint. lots of paint.

618103 D'aww, though I'm not really one for romance / shipping, the idea sounds charming as hl. I won't be using it since I would totally suck at writing romance, but that is an idea I'd love to see in a story.

You can be as vague or as specific as you want.

Alright. What if something happened between two characters, and that causes some other shit to happen, and then they need to get help from that one guy if they want to stop this thing, you know what I'm saying?

Nightmare Moon stalks a filly in her dreams. Probably been done already, right?

After that fiasco with Lightning Dust at the Wonderbolts Academy, Rainbow Dash thinks it would be a good idea to show that egotistical jerk (which, coming from her, is saying something!) a lesson. A lesson on friendship, not on getting punched in the face. I need to clarify that, because that's sort of what it turns into.

The two are just too competitive, and Lightning Dust is just enough like Rainbow that she can't make any progress without getting angry at this pony that seems to be an exaggeration all her bad qualities (and Lightning Dust just gets angry). Still wanting to do the right thing, she figures she should outsource her friendshipping to somepony more level-headed, but awesome enough that Lightning Dust wouldn't completely ignore them.

Twilight Sparkle, of course, is the perfect pony for this.
The world needs more TwiDust.