I'm facing a rules problem/question with the Winter Witch prestige class.
The WW ability.
Unearthly Cold (Su): At 8th level, a winter witch’s spells,
spell-like abilities, and supernatural abilities that deal cold
damage become horrendously cold. Half the cold damage
caused by these effects comes from an otherworldly
power and is not subject to being reduced by resistance or
immunity to cold-based attacks.
The monster having Cold Immunity
Immunity (Ex or Su)
A creature with immunities takes no damage from listed sources. Immunities can also apply to afflictions, conditions, spells (based on school, level, or save type), and other effects. A creature that is immune does not suffer from these effects, or any secondary effects that are triggered due to an immune effect.
Format: Immune acid, fire, paralysis; Location: Defensive Abilities.
or
Energy Immunity and Vulnerability
A creature with energy immunity never takes damage from that energy type. Vulnerability means the creature takes half again as much (+50%) damage as normal from that energy type, regardless of whether a saving throw is allowed or if the save is a success or failure.
So the question we're debating here, is that I have a winter witch character with snowcasting from Frostburn. She tried to make a spell that does no damage, just effects (suffocation) on frost giants as a cold spell. The DM ruled that because immunity says that they are immune to all spells with the cold descriptor, they would be immune to any spell that she made 'cold', even if it did no damage. (snowcasting basically just gives any spell the cold descriptor, which gives her a CL bonus due to her prestige class) My side of the debate is that they are just immune to cold DAMAGE, not side effects from cold spells, and unearthly cold should probably get past that for effects anyhow. (ie. boreal wind is a stronger, cold gust of wind. Even without Unearthly Cold they would just be immune to the cold damage it caused, but not immune to the wind pushing effects.)
Also, technically, by that logic Unearthly Cold would be a total waste since any spell with the cold descriptor they would be totally immune to anyhow and it wouldn't even do damage in the first place, so half of the damage not being cold would be a moot point.
This isn't a heated, angry debate, just one where we're both confused and don't really know what the answer is. It happened a couple of days ago in our game and we need to figure this out before we start again. His ruling for that day was that he let me re-choose my action saying how the giants just would laugh off the mass suffocation spell since it now had a cold descriptor (so I chose to cast it normally instead).