The Species 8472 planet killer fires on a Borg-assimilated planet.
This is the end result.
The Species 8472 planet killer was a weapon used by Species 8472 to destroy planets. A devastatingly powerful weapon, Species 8472 used it with extremely potent results against planets that has been assimilated by the Borg in their campaign to exterminate them. (VOY: "Scorpion")
The weapon was not a single entity, but was formed by several Species 8472 vessels working together; eight bioships and one energy-focusing ship. The 8 bioships would form a ring around the energy-focusing ship and fire on it. The energy-focusing ship amplified and focused the energy bolts of the 8 bioships into one huge bolt. It was this 'super energy bolt' that destroyed the planet.
Using this weapon, Species 8472 systematically annihilated planet after planet in Borg space. In a battle that occurred in the region of Borg space which the Borg designated Matrix 010, Grid 19, eight planets fell to it. (VOY: "Scorpion, Part II")
Combined with the absolute superiority of Species 8472's technology to that of the Borg, the complete inability of the Borg to develop any kind of defense against them, and their immunity to assimilation, the Species 8472 planet killer made the extermination of the Borg a certainty; if Captain Kathryn Janeway and the crew of the USS Voyager had not been forced to intervene and supply the Borg with a weapon against which Species 8472 had no defense and to which they were vulnerable, the Borg would have been made no more than an unpleasant memory. (VOY: "Scorpion")