Use your coins, however if you do not have the Artificer yet, hang on and keep saving those coins. The very first thing you may discover dotted around the phases are these odd Lunar Plants. They will open up and provide you an item if you provide them one Lunar Coin. I truthfully do not know adequate about the items they may include to inform you if this deserves it, I can merely advise you that you require great deals of coins to get a character. That is up to you if you desire to invest them on Lunar Plants.