Text (US+errata): When an opponent casts a spell, if ~this~ is an enchantment, ~this~ becomes a 1/1 Bird creature with flying. [Oracle 2009/07/08]
When it turns into a creature, it no longer counts as an enchantment. [Urza's Saga Rule Page]
It changes even if the spell is countered. [D'Angelo 1999/05/01]
It becomes a creature when the spell is announced, which is before that spell resolves. A Disenchant cannot be used to destroy this card, since it will no longer be an enchantment when the Disenchant resolves. [D'Angelo 1999/05/01]
