Reproduction, it's a perfectly valid thing that makes total sense. When a mare and stallion love each other very much... Blah... Blah... Blah. Here's a foal. That's how it's supposed to work. Except for when it does not.
Terror begins after Twilight and her friends make a horrifying discovery during a trip to the castle of the two sisters. Now trapped within the ruined castle, they swiftly learn the darkness is the last thing to fear.
After a long day at work Pinkie Pie discovers something is troubling her new marefriend. So, Pinkie does what she does best, tries to turn that frown upside down.
Late one evening, a very troubled Pinkie Pie is visited by a pony she knows all too well. Yet, can she bare to face the reason, and realise that what she's done far exceeds simple fun and games?
With Rarity and Applejack both having coltfriends for their own. Pinkie throws an party with the only pony who can come is Rainbow Dash. With the Rainbow for some unknown reason keeps looking at Pinkie in an new light.