Ice Bro

Ice Bros. are rare sub-species of Hammer Bro. introduced in World 3 of New Super Mario Bros. Wii. Upon encounter, Ice Bros. seem like ordinary Hammer Bros., but with light blue shoes, shells and helmets. And instead of throwing hammers, they will throw ice balls at their enemies. If Mario, Luigi, Blue Toad or Yellow Toad get hit by one of their ice balls, they will freeze in a block of ice for a moment. These Ice Bros. are considered one of the most elite fighters of the Koopa Troop.

New Super Mario Bros. Wii
Ice Bros. appear in World 3 of New Super Mario Bros. Wii. As aforementioned, they will use ice balls as weapons to harm and freeze the gang (even freezing other enemies, including others of their species). Like most of their related species, they usually attack in a group of their members. If a Yoshi catches one of their ice balls, the Yoshi can spit it out in the form of a blue fireball that freezes anything in its path.

Paper Mario 3DS
Ice Bros. are scheduled to appear in the upcoming Paper Mario game for Nintendo 3DS. They can be seen as enemies in the snow level.

Trivia

 * Ice Bros. are polar opposites of Fire Bros., similar to the comparison of a Fire Flower and Ice Flower.