10% chance per Freezing card in your hand to discard all swift/quick cards from enemy hand. Rarity of card determines damage done per card discarded. Common: 1, Uncommon: 3, Rare: 5.
Cold Arrow, Glacial Temple, Ice Revenant, Ice Dragon, Blizzard are some current cards that would get the keyword.
Also, the card with the keyword would be immune to Flare Attack as well.
Alternatively, instead of swift/quick cards, it could work on burning cards, kinda like how holy's effect targets undead cards.