When an opponent casts a creature spell, if Opal Guardian is an enchantment, Opal Guardian becomes a 3/4 Gargoyle creature with flying and protection from red.
It was a moment in time, cast in stone—a moment whose time had come again.
2006-09-25
A face-down creature spell will cause Opal Guardian's ability to trigger (if it's an enchantment).
2006-09-25
After the triggered ability resolves, Opal Guardian is no longer an enchantment.
2006-09-25
Guardian's effect doesn't wear off.
2008-08-01
A noncreature permanent that turns into a creature can attack, and its {T} abilities can be activated, only if its controller has continuously controlled that permanent since the beginning of their most recent turn. It doesn't matter how long the permanent has been a creature.