This weapon creates portal 2 portals (Right above where it lands and another one higher than the first one) then spawns a Companion Cube in between to travel in and out of the two portal creating its speed. After some time, the two portals dissolve and the accelerating cube smashes into the ground, dealing damage.
Much like the first tier, it sends two portals for a cube to traverse in, except the gap between the two portals is much bigger, giving the cube more time to speed up and deal more damage.