I only had two decks so far that did pretty well in the gold league, one was a mono-fire and recently a fire-water combo when Oracle gave me steam machines (57 wins). Those don't work too well for me when I play myself but I think they are pretty deadly for an Arena deck in the gold league, upgraded they become mean machines, especially together with high HP, double mark and double draw. Find a decent mix of fire and water quanta, also depending on the other cards you throw in. Which in my case were a couple of freezes and purifies, three rage potions, four deflags/explosions, one fire and one ice shield and one Fahrenheit and one upgraded octopus for good measure.