There's something I may have missed but we can't stack blocks up can we? and what if we were to dig them out again?
Basically, the world in minicraft is divided into 3 layers:
there's the 'aboveground' part, which consists of stone and trees. this layer blocks movement, but can be removed with the appropriate tool, creating a 'ground' level tile
There's the 'ground' part, which consists of Grass, Dirt, (flowers?), and Sand. This layer can be removed with the appropriate tool, creating a hole, BUT only if there's no 'aboveground' in the same tile(e.g., you can't remove a dirt that's under a tree). this layer doesn't impede movement at all
and finally, there's the 'holes' these are either normal holes or water. It can be filled in with a dirt or sand, creating a 'ground' level tile. This layer impedes movement for mobs, and water drains your stamina(if your stamina reaches 0, then it decreases your health instead)
So, no stacking, except for the 'aboveground' layer, which only occurs naturally anyway(you can't place stone)