purifies arent enough because he will deck you out, the bit of poison is to counteract you bringing your own eternity, rememeber, the FG deck is doubled.
The false god only has 113 cards in his deck because he draws seven at the beginning. FGs draw two cards per turn so he can last 57 turns. With an eternity and photon bouncing, you can easily outlast that. Your false god can't photon bounce himself because he has no creatures and only one eternity and FGs draw twice per turn. A few purifies, sanctuaries, a photon, and an eternity can easily beat this god.
Of course, I'm only talking about a easy counter if you know you'll fight him. If he's added to the list of other FGs and it's random who you fight, then he could be a bit of a problem. His deck is just pretty easily countered if you know what you're up against.