From the Super Mario Wiki
An Ice Bomb is an attack item found in Super Mario RPG: Legend of the Seven Stars. It can be bought only in Seaside Town (before fighting Yaridovich) or can be obtained by using Yoshi Cookies on certain enemies. Mario and his party may also be rewarded with Ice Bombs from defeating Machine Made Bowyers. The Ice Bomb, when used, deals 140 HP of damage to enemies. It works well on fire-based enemies, and deals double damage against enemies weak to ice, but does no damage to ice-resistant ones.
In The Super Mario Bros. Super Show! episode "Koopa Klaus", Koopa Klaus himself used Ice Bombs to freeze over Santa's workshop. However, the Ice Bombs in question were never seen, leaving their actual appearance to be a mystery.