The Retroactive Cannon (or 'Ret-Can') is the most lethal weapon in the Time Variance Authority's arsenal. It is designed to bombard an individual with anti-temporal rays, unraveling them backwards through time and erasing them from all reality.
The She-Hulk was given the harsh sentence of being erased from reality via the Ret-Can for her offenses against the timestream. However, the villain Clockwise gained control of it and began erasing other heroes from reality. It was only through the combined efforts of She-Hulk and Southpaw that Clockwise was stopped.
- The Ret-Can appears to be a fairly obvious reference to the Retcon (or retroactive continuity), the practice used by storytellers to add previously unknown material to an event in a previous story.