I think that in the game there should be blocks that, when not connected to another block, collapsed. This would only be a few blocks, but it would make for some cool structures. It would add an architectural challenge if people wanted to build with these blocks. So i made a few examples in Terraria. 1. Imagine the wood is the collapsable block, and the dirt is a non-collapsable block. In this the wood would not collapse because it is connected to dirt. 2. Same as before except this time, the wood would collapse because it is not connected to the dirt: 3. Finally, there could be materials that required many more points of contact like in this image: In the game there could be blocks that required hundreds of points of contact, or it could be set manually. This could result in bridges on php serves collapsing into lava as one team broke it's points of contact with the sides, or just a building challenge. Let me know if you like it.
