Welcome! If you're using the deck I think you are (6 poison, 6 mummy, 4 dragon, 14 pillar), then you should grind AI3. That deck doesn't work too well in the arena. Also, playing bronze lowers your score. A decent FG grinder that isn't too expensive would probably be RoL/Hope, with only 6 upgrades. Liquid Antimatter is unupped but doesn't work too well.