Snow Globe

The Snow Globe is a Hardmode item used to summon the Frost Legion (an event similar to the Goblin Invasion, though harder). It can be obtained from opening Presents in Hardmode worlds during the Christmas season (December 15th through 31st, based on your computer's time setting), but can be used in any world at any time. The chance of getting a Snow Globe in a Present is 1/14, or 7.14%.

Tips
Or they can be considered the hardmode counterpart of the goblin army.
 * The Frost Legion should only be summoned once the player has acquired Hardmode gear. They are considerably stronger than the Goblin invasion.