Slime

Other than being used as a crafting recipe for sticky pistons, it could also be applied to all physical blocks (meaning it exclude water and air). This can be applied to all surface, unlike redstone, with an exception of in water. The slime allow blocks to stick to one another. This can allow mobs to get stuck if they run into a patch applied to the ground. If the player get stuck, the only way to break out is to destroy the block they are stuck to. The slime could also help miners by making blocks that follow physics like sand and gravel "stick" themselves to the ceiling of the tunnel and prevent them from collapsing. The slime could allow blocks that get stuck together to be pushed by one sticky piston, since they are all stuck to the block connected to the piston. The more blocks connected to the sticky piston the more strain the piston have, so the slower it functions. The maximum amout of blocks connected to a piston at any one time is six.