No, you can't, but you could make an onhealthchange script checking if both creatures are players and then multiply the dmg by 2.
if ((damage.primary.value < 0 || damage.secondary.value < 0) && caster) {
Player* targetPlayer = target->getPlayer();
if (targetPlayer && caster->getPlayer() && targetPlayer->getSkull() != SKULL_BLACK) {
damage.primary.value /= 2;
damage.secondary.value /= 2;
}
}
from:
damage.primary.value /= 2;
damage.secondary.value /= 2;
to:
damage.primary.value /= 1;
damage.secondary.value /= 1;
