The idea for Mash Blocks stems from a lack of theme supportive decorative blocks in the game. Perhaps you want blocks that look like appliances, furniture, cabinetry, etc. and there just isn't really much available that fits the bill. Mash blocks are designed to be pushed together into the same block space as each other or as regular blocks using pistons and are designed in such a way as to create a multitude of theme oriented results. For example, one of the Mash blocks could be a dice block, another could be also white, a bit larger but a tad shorter, exposing the top of whatever block it's mashed with. Together, the two look like a stove with the 4 black circles on top representing the burners. I haven't come up with all the different mash blocks and how they would go together. A fair bit of thought would have to go into it, but it is a way to make a few decorative blocks serve a multitude of purposes. With respect to the game mechanics, one way to work around space sharing restrictions would be to have Mash Blocks have a one item (block only) inventory and have the game visually represent both the mash block and the block in it's inventory at the same time, but count the ID as being the mash block. In this case, pistons would not be necessary to merge the blocks. This way, one could make a kitchen that looks more like a kitchen, a living room that looks more like a living room, etc. which may not be important to every Minecrafter, but I know there's more than a few out there that would like to give more personality to their creations.