Hmm, what do you mean?
Firstly, ET can't search for AOCP; you have to have it in your hand already
If you mean playing it before they block
It could win a battle if you play it and it kills all of your opponent's evil characters, so they can't block.
It may not work if they have a protection fort and not all of their evil characters die
It may not work if they have some evil characters in their hand they can block with
It may not work if they have some other forms of stopping you, such as Burial, Unholy Writ, Christian Martyr, etc.
If you mean after they block
It could win the battle.
It may not if they can negate it (assuming it isn't the promo)
It may not if they have other forms of stopping you (see above)
It may not if it doesn't effect them (ignore or immune)
It may not if they have Unknown Nation active.