Opal Champion

Enchantment    (CMC:3)

When one of your opponents successfully casts a creature spell, if Opal Champion is an enchantment, Opal Champion becomes a 3/3 creature with first strike that counts as a Knight.

16 GU • ENEdward P. Beard, Jr.

™ & © 1993—1999 Wizards of the Coast

Legal in: Urza Block,Legacy,Vintage,Commander

Oracle Text (click to copy):

Opal Champion {2}{W} Enchantment When an opponent casts a creature spell, if Opal Champion is an enchantment, Opal Champion becomes a 3/3 Knight creature with first strike.

---

View this MTG card on Gatherer

10/4/2004
It triggers when the spell is cast, so it becomes a creature before the spell resolves. A creature that would destroy an enchantment when it enters the battlefield can't be used to destroy this card, since it will no longer be an enchantment when the creature enters the battlefield.
10/4/2004
When it turns into a creature, it is no longer an enchantment.
10/4/2004
It changes into a creature even if the spell is countered.
4/1/2008
A "creature spell" is any spell with the type Creature, even if it has other types such as Artifact or Enchantment. Older cards of type Summon are also Creature spells.
8/1/2008
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 his or her most recent turn. It doesn't matter how long the permanent has been a creature.

---

Card Opal Champion is not on TCGPlayer.