Opal Avenger
Urza's Legacy — rare
Enchantment
Opal Avenger rulings:
2008-08-01: 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.
2004-10-04: When it turns into a creature, it is no longer an enchantment.