Winter Gift is a consumable first introduced during WinterFest 2013. They randomly spawn in ten minute intervals in worlds (the more people, the more spawn, just like Fireworks and Comet Dust). They can also be obtained from harvesting a Giving Tree at 0%.
The Winter Gift can be used on the Growch to make his heart bigger and unlock new items faster or used on other players to give them the consumable itself. If a player uses it on themselves, they will get a low rarity item.