Remains in play "The Horror" , how to remove?

[ATOEtalGeek]

This question is though - can a card that doesn't specifically remove a remains-in-play mystery card be used to remove a remains-in-play mystery card once that card is in play? I'm referring to the fact that certain cards, such as Daybreak, actually say it targets a remains-in-play mystery, while others do not. Why specify on some cards and not all if it's intended that none of them be limited?

I included this in my other post on random questions. It seems to me that the only way to remove a remains-in-play mystery card once it is in play is to use a card or ability that specifically targets a remains-in-play mystery. Anyone know of an official ruling?