Mossy Cobblestone is a red brown building-block with a stone-chip-pattern and a bit of green moss that you can craft in your Crafting Menu (default key "q") after finding and learning the according rare crafting Recipe for this block.
The rare crafting Recipe for this block can be discovered in Treasure Chests that randomly spawn in darkness, especially in Stone Treasure Chests that spawn on blocks of the Fossil layer underground, or in Obsidian Treasure Chests that spawn on blocks of the Stalactite layer underground.
Recipes can also be learned in player-created Adventures.
In order to permanently add the recipe to your crafting menu (and so it can be carried over to all other Creativerse gameworlds like all rare and store-bought Recipes), this recipe has to be learned at first by right-clicking on it in your inventory/bag or dragging it with the left mouse-button over your player character model on the right side of the inventory.
To craft 8 blocks of Mossy Cobblestones at a time you'll need (as of R44 in June 2017):
- 3 blocks of Canyonstone, Ruddy Canyonstone or Dark Canyonstone mined from Canyons which requires at least a Stone Mining Cell to be equipped
- 1 Stone Rod made of Stone, Limestone or Bedrock in a Processor
- 2 Melted Wax made of Beeswax in a Forge or looted from Wood Treasure Chests or Stone Treasure Chests
- 4 Moss taken from Ashenwood trees, Weepwood trees or Weepwood Logs, which does not require any Power Cells