Snowfall

Snowfall is a unobtainable pre-Hard Mode block that falls during a Blizzard. Every 5 in-game hours since the start of a Blizzard, all blocks inside all Snow Biomes in the world exposed to direct sunlight, with no blocks above them, will be covered with a layer of Snowfall blocks. Snowfall blocks look exactly like snow blocks, and take the same time to be mined, but when mined drop nothing.

Snowfall follows its own physics. A hill made from Snowfall blocks cannot be steeper than 22.5 degrees. If the hill is steeper, the blocks will slide down the hill until the angle is 22.5 degrees or less. The area under Floating Islands can be covered in snow this way.

If half of the world's surface (Floating Islands count as the world's surface, but the blocks below do not) is covered in snow, ice, Snowfall or Frost, the whole world will be thrown into an everlasting Blizzard. Snowfall blocks count as candidates for Snow Biomes, so shortly after this the whole surface of the world will be a Snow Biome.

If a player is walking on the surface of the world as a layer of snow falls, their legs will be trapped in the Snowfall blocks. They cannot move until they free themselves with a pickaxe, and they will get the Suffocation debuff.