When an opponent casts a spell, if this permanent is an enchantment, it becomes a 3/3 Illusion creature with flying and "At the beginning of your upkeep, sacrifice this creature unless you pay ."
(01/08/2008)
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.
(04/10/2004)
When it turns into a creature, it is no longer an enchantment.
(04/10/2004)
You choose whether to pay or not on resolution. If not, then you sacrifice the creature. You can choose to not pay if you do not control the creature on resolution.
(04/10/2004)
It triggers when the spell is cast, which means it becomes a creature before that spell resolves.
(04/10/2004)
It changes into a creature even if the spell is countered.
