Opal Guardian
Enchantment
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.
Illustrated by
Time Spiral#30RareEnglishLegality
Rulings
Sep 25, 2006
Guardian’s effect doesn’t wear off.
Sep 25, 2006
After the triggered ability resolves, Opal Guardian is no longer an enchantment.
Sep 25, 2006
A face-down creature spell will cause Opal Guardian’s ability to trigger (if it’s an enchantment).
Aug 1, 2008
A noncreature permanent that turns into a creature can attack, and its 
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.