Definition of * words:
Headcanons:
Headcanons are ideas from information gathered from books, Television shows, the internet, etc.
Fandom:
The community that surrounds a certain thing with fans.
Mane 6
The Mane 6 consists of six mares that are known as the Elements Of Harmony.
Consisting of two Earth ponies, two pegusi, One unicorn and one alicorn.
The Earth Ponies in the Mane 6 are known to be the Element of Laughter, and the Element of Honesty.
Their pony representations are well known to be the bubbly and fun-loving, Pinkie Pie and the strong and hard-working Apple Jack. Despite them not having any wings or horns, they are able to help the other four by using their hooves.
The Pegusi in the Mane 6 are known to be the Element of Kindness, and the Element of Honesty.
Their pony representations are commonly known to be the shy, and caring Fluttershy, and the Energetic and athletic Rainbow Dash.
With their wings, they help out by looking from the clouds that some Unicorns and Earth Ponies can't reach. Fluttershy doesn't like being in high places though!
The Unicorn in the Mane 6 is the one who represents the Element of Generosity.
The pony representation is known to be the one of the Diva/Fashionista Rarity. She may not look as if she would be generous, but she is as caring of her friends the same way she feels about clothing. Her horn isn't well in spells, but she is great at handling or handing things to her friends, even if it means getting dirty.
The Alicorn of the Mane 6 is now known to be the Princess of Friendship and the Element of Magic at the same time.
She's the one and only Twilight Sparkle, a super-smart Alicorn who helps out her friends with her brains.
Known as one of the four good Princesses in Equestria, she lives in a crystal treehouse in Ponyville. Her horn is as good as handling spells as she is with helping her friends out no matter what.
Relatives
The Apple family are all of the relatives of Apple Jack, They consist and live all around Equestria, but most likely they live in Appleoosa.
They appear in the episode where the whole family comes together at Sweet Apple Acres for one of the Apple family reunions. The Apple family that live in Sweet Apple Acres consist of Granny Smith, Big Mac, Apple Bloom and, of course, Apple Jack!
The Pie family are all the relatives of Pinkie Pie, they live on a rock farm somewhere in Equestria. They don't appear much in the show but one of Pinkie Pie's sisters, Maud Pie, has an episode about her coming to Ponyville to visit Pinkie in Season 4. Her whole family is shown in the episode where the Cutie Mark Crusaders are running around Ponyville asking the Mane 6 how they got their cutie marks.
Twilight's Family is consisting of her brother Shining Armor, her mother Twilight Velvet, Her sister-in-law Princess Cadence and Twilight's Father who doesn't have a specified name. Her parents are seen in the Royal Canterlot Wedding and in the episode where the CMC are asking for how they got their cutie marks. Her sister-in-law and brother are seen in quite a lot of episodes, but they have a two-part episode dedicated to how Cadence and Shining Armor got married. Quite a family!
Cutie Mark Crusaders
The Cutie Mark Crusaders are three fillies trying everything from A-Z to find their destiny/cutie marks.
Apple Bloom is the sister of Apple Jack, she's sassy and sweet, she tries to find interests in baking or helping out at the farm to find her destiny/cutie mark. In the process, she helps her companions Sweetie Belle and Scootaloo find their cutie marks also. Her bow from most *headcanons is said to be given by her mother. We won't get into detail about that.
Sweetie Belle is the sister of Rarity, she's caring and helpful, she tries to find her destiny by helping her sister or learning magic with Twilight. Around that line, she models clothes for her sister and she is learning how to control and use her magic by the help of the Princess of Friendship. Her parents were shown in episodes along the seasons of MLP, but we don't know their names.
Scootaloo looks up to Rainbow Dash as an Idol, and in return, Rainbow treats Scootaloo like a little sister. She tries to find her cutie mark by doing sports and more. Her parents aren't verified in the show, and she is said to be an orphan from most headcanons in the *fandom. She is called Chicken because she doesn't know how to fly at her age. She travels around Ponyville with a scooter, and Sweetie Belle and Apple Bloom tag along either in a wagon that's being pulled by her, or on snowboards that are also being pulled by Scootaloo.
The Princesses of Equestria
We can't forget the Princesses that ruled over Equestria can we? Of course not!
Princess Celestia is the eldest sister of the two, she is the Princess that welcomes the day and raises the sun. It was hard for her to send her little sister and only sibling to the moon, but she had to do it to save Equestria from eternal darkness. She is known to be wise and thoughtful of her duties, she has helped Twilight from the day she got her cutie mark to the day she became a Princess. She loves her sister very much and cares for her, trying to forget Nightmare Moon and the pain that had consumed her when her sister was gone.
Princess Luna, the youngest of the two sisters, she is the Princess that lowers the moon and raises the moon. Being overtaken by Nightmare Moon because of jealousy that she was living in her sister's shadow, she was sent to the moon. She is known to be a regal and judgmental princess. She loves her sister and is trying to forget how she become Nightmare Moon, she is now treated as equally as her sister.
Princess Cadence is the ruler of the Crystal Kingdom, she is the Princess of Love. She is married to Shining Armor, Princess Twilight Sparkle's brother. On her wedding day, she was trapped in a dungeon by Queen Chrysalis. Chrysalis had posed as Princess Cadence marry Shining Armor just for power. It had failed. She is the sister-in-law of Twilight Sparkle and they get along very well.
Others
Cheese Sandwhich is another Party Pony that competed with Pinkie Pie. His cutie mark is, of course, a cheese sandwhich,
Discord is the lord of chaos.
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We don't have every single pony in the seasons, but we have just the basic ponies that you need to know.