Frozen Wild Shape( Frostburn, p. 48)
You can assume the form of magical beasts with the cold subtype.
Base Fortitude save bonus +6, wild shape ability,
You may use your wild shape ability to assume the form of any magical beast with the cold subtype. Your new form must still fall within the size limitations of your wild shape ability. As with the standard wild shape ability, you do not gain any of the extraordinary special qualities or any supernatural abilities possessed by the new form, with the exception of the cold subtype. This subtype grants you immunity to cold but vulnerability to fire, which means you take half again as much (+50%) damage as normal fromfirewhile in a frozen wild shape, regardless of whether a saving throw is allowed, or if the save is a success or failure. Possible cold magical beasts from the Monster Manual include cryohydras (Huge wild shape required), frost worms (Huge wild shape required), and winter wolves. Possible cold magical beasts from Monster Manual II include frost salamanders. Possible cold magical beasts from this book include brantas (Large wild shape required), ice toads (Large wild shape required), urskans (Large wild shape required), and tlalusks (Huge wild shape required).