it would be an interesting twist on the game if the wisps that sometimes float into proximity with the battle circle actually floated into it and healed (or recharged the mana ) of whatever they touched - players or enemies.
it would add an extra dimension of challenge and strategy. You'd have to take into account what wisps were around when you started fights and whether they'd impact the battle, you'd get an extra boost of health once in a while and so would what you were fighting.