Hard mode has the spheres going in two different directions, which makes it a little bit easier in the beginning because you can get bigger chain. When marbles are being destroyed on one side, expand the chain by shooting a marble toward the other side. It's easy to get a twelve or more chain this way. The strategy for Hard mode in the beginning is just to group pairs of at least two red, at least two blue, and at least two red. Then, destroy a set in the middle of this arrangement in each path.