The highest amulet is the witch star amulet. It gives really good cards, but the lowest health. I think for each school their should be an amulet that provides unique spells that help a certain school, and a high health amount given determined for each school, such as ice gets really high health and storm would get the lowest but it still would be high. In addition, instead of being sold by crowns it should be dropped by a special boss for each school, like on a quest, maybe, or just from certain boss.