WinterFest is a yearly event which is held during late December, lasting for two weeks. During WinterFest, the world GROWCH is inhabited by an NPC named Growch. When enough Winter Gifts are given to him, a few WinterFest items will be unlocked, thus making Growch happy and restricting gifts to be given to him for several hours.
Players can visit the Growch in worlds GROWCH1, GROWCH2, etc, similar to GROWGANOTH. Winter Gifts also spawn in worlds, depending on the amount of people in the world. During this time, the world select music changes.
In order to unlock some items and their recipes, players need to get the Growch's heart to a certain size before those items can be made. All splicable items or items which require a heart size to unlock can only be made during WinterFest.
During WinterFest, normal Ghosts are replaced with the Ghost of Winterfest Past. Upon contact, the player will have the "Frozen" mod active for 2 seconds, which is the same effect caused by a Snowball.