From the Expanded Universe My Little Pony: FIENDship Is Magic #5 comic, Chrysalis and the changelings are shown to have first come into being as a result of a rotten acorn that fell into a tainted magic pond underneath a graveyard. The seed mutated, grew into a carnivorous plant, and when it was cracked open by accident by Starswirl the Bearded O8o6fCF.