After opening the top and throwing the Gravity Shifter up there, let a mine follow it. When it is up there and you cannot see it, throw the Magic Ball up there. Then, throw a Grenade. They will combine, then in a flash of light there will be a grenade that is purple and three times the size of the green variety. You cannot destroy or move it. However, it packs an extremely powerful explosion. There can only be one of them at a time on screen.