A Hero Emerges?

[Phred]

When your opponent declares an attack, he/she randomly selects 1 card from your hand. If it is a Monster Card, Special Summon it on your side of the field. If not, send it to the Graveyard.

Is it's effect refering to each time an opponent declares an attack in the turn it's activated, or only one?

 

[Lord Hades]

...only for one attack, cause it is not a continuos trap card...

 

[DaGuyWitBluGlasses]

A Hero Emerges is activated in response to an attack. (Like Mirror Force)

 

[Phred]

Ok ok, I get it, the text
was just a bit ambiguous
A Hero Emerges lacks "You can only activate this card when your opponent's monster declares an attack"