This is part of the planned alternate universe comic by Chedx, planned for a 2019 release date.
Here are some pictures that give you some insight into the world of “The Storm Kingdom”.
The Storm King is utilizing and weaponizing everycreature in his kingdom, giving him a powerful and diverse military.
The military includes
“Storm Creatures, Ponies, Dragons, Changelings, Griffons, Yaks, Parrots, Abyssinians and Hippogriffs”
General Tempest Shadow
https://derpibooru.org/1738592?q=general+Tempest+Shadow&sd=desc&sf=created_at
The Storm Six
https://derpibooru.org/1738600?q=storm+kingdom
If anything they were the ones who created the Crysal.
It looks like they are willingly serving him. (No Crystal of Light on their foreheads, so, no mind control)