Icengard mobs. It is one of the four items needed in order to craft the Frost Staff. It does have several solitary uses, which will make it able to be a plain item on it's own if there are some left over after crafting.
When right-clicked, it will spawn an Ice block. While mining Snow, Snow Blocks, Ice, or Tundra trees, it will speed up the mining process by 55% and have Silk Touch effects.