Each item in Minecraft has a unique ID assigned to it, known as an item ID, this can be used in commands to spawn the item into the game. The item ID for mossy cobblestone slab in Minecraft is shown below:
The Mossy Cobblestone Slab item can be spawned in Minecraft with the below command. Cheats must be enabled before this will work.
|Max Stack Size||64|
|6x Mossy Cobblestone Slab|