go to advanced - gameplay constants
then search "spells - ethereal heal bonus"
then change that value. for example:
40% more spell damage = 140% damage = 1.40
76% more spell damage = 176% damage = 1.76
56% LESS damage = 44% damage = 0.44
Not that this will apply for ALL units that are ethereal, no matter how or why they got ethereal
Actually its "EtherealDamageBonus".....