Needs review
Source: Frostburn

Description: Your cold spells are so cold that they can damage creatures normally resistant or immune to cold.

Prerequisites:

You can only apply this metamagic feat to spells with the cold descriptor. Piercing cold spells are so horribly cold that they are capable of damaging creatures normally unharmed by or resistant to cold. Piercing cold spells completely ignore any resistance to cold a creature possesses, bypassing this resistance and dealing damage to the target as if it did not possess any resistance to cold at all. They are still entitled to whatever other defenses the attack allows (such as saving throws and spell resistance).

Creatures normally immune to cold can be damaged by piercing cold spells as well. Piercing cold spells deal half damage to these creatures (or one-quarter on a successful saving throw). For example, Mialee casts a piercing cold cone of cold at a night hag, a creature normally immune to cold. She makes her level check to penetrate the night hag's spell resistance, but the night hag makes her Reflex save against the spell. Mialee rolls the dice, and her cone of cold deals 42 points of cold damage; since the night hag made her save, the damage is halved to 21 points. This damage is then halved again (since the night hag is normally immune to cold), and 10 points of cold damage are actually dealt to the night hag, who is both shocked and enraged at this unexpected turn of events.

Creatures with the cold subtype can tell that a piercing cold spell is colder than normal, but they remain undamaged by the attack.

Creatures with the fire subtype who are damaged by a piercing cold spell take double normal damage instead of the usual +50%.

A piercing cold spell uses up a spell slot one level higher than the spell's actual level.