Sombra, Discord, Luna, Chrysalis, and Celestia. They're are many other theories revolving these six so I decided to make one. I think they where the orignal elements of Harmony. Right now your probably thinking what about the sixth, well....I suggest that's Luna and Celestia's older sister, Cadance's mother. Here's how the theories go.
Honesty - I will go with a place holder name of some sort, maybe Venus, she was the first to go. After giving birth to Cadance she became ill and over worked. Leader of the Crystal empire, she found put her needs where less important than her kingdom. Though over the years she got progressively worse. Ending i