Text (AR+errata): 2/2. ; Flash. ; When ~this~ enters the battlefield, prevent all damage that would be dealt to artifact creatures this turn. [Oracle 2009/07/08]
It does not lock in the affected creatures when the triggered ability resolves. It applies to all creatures during that turn, even if they enter play or become artifact creatures after the ability resolves. [Alara Reborn FAQ 2009/04/30]
