Pathblaster

...Spartan Laser?

The Pathblaster is an enormous Decepticon weapon.

Fiction

Marvel UK continuity

In development during the Time Wars, the Pathblaster was being stored on the shuttle used by the Wreckers and the Mayhem Attack Squad. After destroying a chunk of Galvatron's head (a considerable feat, bearing in mind how much the guy had been shot by that time), the gun exploded in Roadbuster's hands. Time Wars

The Pathblaster, Roadbuster, and half of Galvatron's face were never seen again. Although only shown a handful of times, it was this intervention that gave Galvatron the last little step into insanity.