Update:WinterFest/2013

Dec 21st: It's WinterFest in Growtopia until December 31st!
It's a magical season of gifts and wonder... for everyone except the Growch! Which is really to bad considering he invented a bunch of cool new items, and he won't share them with Growtopia.
Maybe if we all show him the holiday spirit, he'll let us make the new items.
- @Seth and @Hamumu

Items

Item	Heart Size	Recipe
Inviso-Block	0	Unobtainable; cannot be obtained by regular means. An invisible block used to allow players to step on the Growch. Also used in its parkour and WOLFWORLD_6.
Doohickey	0	Can be obtained from the What's that? special event. One has 10 seconds to find 1 dropped Doohickey.
Winter Gift	0	Spawns in regular worlds like Comet Dust. The more people, the more likely it is to spawn. Up to 4 can be dropped from harvesting its tree, made by splicing: • Sheet Music: Flat Piano + Sheet Music: Flat Bass → During WinterFest 2013 only!
Weather Machine - Snowy	0	1 can be obtained from purchasing the item itself for 10,000 gems in the Growtopia Store.
Snowy Rocks	0	Up to 4 can be dropped from harvesting its tree, made by splicing: • Rock + Ice
Tangyuan	1	Up to 4 can be dropped from harvesting its tree, made by splicing: • Wheat + Water Bucket
Elf Hat	1	1 can be dropped from combining: • Transmog Crystal (×1) • Santa Hat (×1) • Green Block (×20) in any Chemical Combiner.
Candy Cane Block	2	Up to 4 can be dropped from harvesting its tree, made by splicing: • White Block + Red Wood Wall
Snowball	3	Up to 4 can be dropped from harvesting its tree, made by splicing: • Ice + Water Bucket
Festivus Pole	3	Up to 4 can be dropped from harvesting its tree, made by splicing: • Checkpoint + Wooden Platform
Giant Candle	4	Up to 4 can be dropped from harvesting its tree, made by splicing: • Climbing Vine + Torch
Buckskin Pants	4	Up to 4 can be dropped from harvesting its tree, made by splicing: • Cave Entrance + Brown Block
Buckskin Jacket	5	Up to 4 can be dropped from harvesting its tree, made by splicing: • Cave Entrance + Barrel
Candy Cane Fence	5	Up to 4 can be dropped from harvesting its tree, made by splicing: • Wrought-Iron Fence + Sugar Cane
Buckskin Hood	6	Up to 4 can be dropped from harvesting its tree, made by splicing: • Cave Entrance + Rock Platform
Antler Hat	6	Up to 4 can be dropped from harvesting its tree, made by splicing: • Cuzco Wall Mount + Das Red Balloon
Glowing Nose	7	1 can be dropped from combining: • Chemical B (×12) • Chemical R (×10) • Chemical Y (×4) in any Chemical Combiner.
Ice Dragon Hand	8	1 can be dropped from combining: • Dragon Hand (×1) • Snowball (×20) • Transmog Crystal (×1) in any Chemical Combiner.
Yeonnalligi	9	Up to 4 can be dropped from harvesting its tree, made by splicing: • Blue Portal + Orange Portal
Holiday Gift Box	10	Up to 4 can be dropped from harvesting its tree, made by splicing: • Treasure Chest + Slot Machine
Polar Bear Leash	10	Can be purchased from Nutcracker for 30 World Locks. → New recipe added as part of WinterFest 2019!

Trivia

A FAQ thread was posted by ex-developer Hamumu on the date of WinterFest 2013's release, answering questions players might have about how Growch's system works.