My Gastly currently has Psywave and Night Shade as its primary damaging moves yet for example when I use Night Shade on a Physic Type it doesn't do increased damage. I am pretty sure that just because it doesn't have a fixed PWR value it shouldn't do basic damage, I'm guessing it works the other way around as well, say I should only do half the damage, it would probably still do 1x the Damage.