>>42348854
They have a vaguely defined emotion based magic. When they're highly charged with positive emotion they get super shiny and translucent. Also they're somehow tied to the crystal heart. The crystal visual effect can be temporarily be cast onto non-crystal ponies by major magical releases by the magic of [s]marketing buy our toys[/s] the crystal heart.

I kinda wonder how a crystalled snow poner would look. Also, crystal ponies were criminally underdeveloped and underused but it's still nothing compared to bats getting the shaft.