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


."
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.