Phyrexian Furnace is a cheap artifact that mostly replaces itself: pay {1} and sacrifice it to exile a card from a graveyard and draw a card. Their deck gives it little graveyard recursion to attack, so treat it as a smooth cantrip rather than hate. Naturalize stays in the sideboard, since they have no artifacts or enchantments on the battlefield for it to hit. Even their Caller of the Claw Bear tokens are creatures, so Naturalize can't target them. Sylvan Library is risky against their aggressive clock and reach (Mogg Fanatic, Siege-Gang Commander, Goblin Sharpshooter), since paying life to dig is dangerous when they're racing you, so both copies come out.