I'm not sure what "normal" damage is in this context. For example, let's say I have a spell that deals 100 cold damage, with a saving throw for half, and I cast this spell against a fire giant. If the fire giant fails it's save, then it takes 150 damage. However, I'm not sure how much damage it takes if it succeeds on the save. Does it take 150 damage or 75 damage?The SRD said:Vulnerability to Energy: Some creatures have vulnerability to a certain kind of energy effect (typically either cold or fire). Such a creature takes half again as much (+50%) damage as normal from the effect, regardless of whether a saving throw is allowed, or if the save is a success or failure.