A Mothership firing its catalyst cannon.
The 'catalyst cannon' is the catastrophically damaging weapon used by the Scrin Motherships.
Perhaps the most powerful energy weapon of a wide variety deployed by the Scrin, the technology behind the catalyst cannon remains unknown, although GDI InOps may hold classified documents on its operation. A direct hit from the cannon is, the vast majority of the time, enough to completely destroy a building. However the weapon deals more damage if the structure attacked is in close proximity to other structures, as these nearby buildings will be subject to a lethal chain reaction. In this way the weapon has been used to raze densely-packed centers of population. For example, one blast was able to incinerate most of Berne.
Fortunately for humanity, Motherships are sufficiently rare and slow moving for this weapon to have been used only a very small number of times.