Hmmm...Good question. |D

The "blessings" were mainly targeted towards the royal children, since they are the offspring of the ones who banished him again. However I think any normal crystal pony in the area can be affected as well. (It's just that most of them don't survive too long when they "recieve" it. The crystal tends to spread through their entire bodies and turn them into statues of corpses. It's already hard enough to contain the marked areas of the siblings. ) 

_{Radiation poisoning? Lol, that's kind of another way to put it. XD}