Hokay, so I've done some brainstorming on what I might like to do in the
MLP: Friendship is Magic universe, and ended up settling on a comic series based around OCs, rather than the current FIM cast.
The basis behind the comics, which will all be relatively short self-contained storylines (or at least that's the plan so far) follows an AU Royal Family; Queen Terra and her twin daughters, Moonlight Eve (the elder) and Aurora Dawn (the younger.) The idea is that Terra sends her daughters off into the world to experience life outside of Canterlot and the Palace, and the comics follow their adventures.
Around Equestria they meet many new and interesting ponies and other creatures, but the four ponies that are going to be a recurring theme are Nightmare and Daydream (actually physically based on a pair of MLP customs I did a couple years back), who are Earth ponies, Strawberry Sky, who is a Pegasus, and Rift, who is a Unicorn.
There are some other characters as well that I'm still working out, but one of them is Tucker, who is a Tiger-Manticore cub, and Artemis, who is a mysterious black wolf who, for some reason, appears to have a Cutie Mark the same as ponies do. I've got the very basic info for Tucker and Artemis spinning in my head while I work out more of the details.
Anyway, here's some pics that I did to help me with visualizing! They were all done via various doll maker games at
Doll Divine in the "animals" section. I can kill SO MUCH TIME on that site, you have no idea... XD;;
Queen Terra:

Queen Terra is actually just a Unicorn, rather than an Alicorn like Princess Celestia/Luna in FIM. Terra's daughters are Alicorns, however, so I suppose she must have some Alicorn or Pegasus in her lineage somewhere... or their father was winged. idk, I haven't really thought about it since so far I don't plan to use him in the stories/comics. lol.
Princess Moonlight Eve:

Princess Eve is the elder twin, a few minutes older than her sister. She's very similar to Aurora in a lot of ways, but is also a lot more reserved than her at times and often takes on the role of "big sister" to protect and comfort her. While Aurora takes after their mother, Eve probably takes after their father more, though they can't know for sure since they hardly knew him.
Dusk:

Dusk is Princess Eve's pet, a black pidgeon. She's calm, collected and behaves in a way befitting of a Royal Pet. Dusk came to live at the Palace as a gift for the Princesses from a visiting dignitary; but since Aurora already had a pet of her own, Dusk quickly settled with Eve. She is good friends with Minka, but avoids the Palace cats.
Princess Aurora Dawn:

Princess Aurora is the younger twin. She is bright, cheerful, and friendly to a fault. She tends to only believe the best in everypony, and has been hurt before because of it. Still, she's a bright spot in the lives of most everyone who knows her. Despite that, she is actually very emotionally dependent on Eve.
Minka:

Minka is Princess Aurora's pet. She is an ordinary rat, and began life in the Palace as a pest, living in the walls and stealing food from the kitchens and pantries. Eventually, humane traps were set to catch the rats for relocation, and Minka was caught in one. Aurora was the first to find her, and as Minka was so friendly to her, insisted that she keep her. Minka is friendly to everyone, very intelligent, but also has a mischievous streak that gets her into trouble sometimes.
Nightmare:

Nightmare (and her cousin, Daydream) both come from Hoofington, where they grew up. Because of her coloration and name, Nightmare was often picked on as a filly, and those who didn't pick on her were afraid of her; rumors circulated about her parentage and possible relation to demon ponies. Because of all of that, Nightmare grew up very quiet and introverted, afraid of what might happen if she tried to speak her mind or confront those who bullied her. Only Daydream was kind to her, and they have been best friends ever since.
Daydream:

Daydream is cousins and best friends with Nightmare. When they were both young, Daydream often stood up for Nightmare and comforted her when she was bullied. Daydream is outgoing, cheerful and makes friends easily-- basically the exact opposite of her cousin. Still, they're as close as two ponies can be and Daydream wouldn't trade that for the world.
Rift:

Rift is originally from Trottingham, and grew up in a high-class home, as his parents were very well off. When he was young, he was somewhat stuck-up about his class in life, a fact that he very much regrets now that he's older and had grown past that phase. Now, Rift is quiet, unassuming, but friendly. He tries his best to work for what he has, even if he's not very good at most manual labor.
Strawberry Sky:

Strawberry Sky hails from Las Pegasus (L.P.), where she lived until she was old enough to strike out on her own. Before that, she had never even set foot on the ground. Strawberry Sky is outgoing, sweet and always looking for adventure, even in the little things.
Tucker:

Tucker is a Tiger-Manticore cub; Tiger-Manticores differ greatly from Lion-Manticores in many physical ways. As a Tiger-Manticore, Tucker lacks the mane, wings and distinctive scorpion-tail of common Manticores. He has stripes over parts of his coat and only a small patch of hair that hangs over his eyes. His tail is much like a tiger's, but lined with multitudes of poisonous stinging barbs. (The doll maker obvsly didn't have those as an option. I'll sketch Tucker out for better reference later.)
Tucker is an orphan, barely surviving on his own in the Everfree Forest after his mother was killed by a hydra. Because of his lot in life, he's becoming quite timid and fearful, when he used to be proud and relatively carefree.
Artemis:

Artemis is an enigma. No one knows where he's from, what, exactly, he is, why he has what appears to be a Cutie Mark, or how he's connected to Princess Nocturne and Princess Aurora. More information and back story for him will be revealed over time.
AND THAT'S WHAT I HAVE SO FAR! :D
Yeah, no Cutie Marks for the ponies yet because I'm still pondering most of them. Strawberry Sky's is a strawberry with little wings, but other than that I haven't decided anything concrete. *facepalm*
EDIT: Raiden MLP icon~ ♥♥♥
EDIT #2: Had to change Nocturne's name, as a character with that name will be appearing in FIM season 3. She is now called Moonlight Eve (just "Eve" for short), and Aurora's name has been lengthened to Aurora Dawn to match (she still just goes by "Aurora", though.)
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