The weapon is a submachine gun that is used by Mara Aramov's men in the final two levels of Syphon Filter 3; it is a powerful and fast firing weapon which can be potentially lethal due to the close quarters that combat occurs in.
Syphon Filter: The Omega Strain
This weapon is called the Marz FMG or Folding Machine Gun. As its name suggests, it can be disguised as a box and unfolded for swift combat, but the lack of iron sights (or poor quality of sights) and its fast firing rate all make it unsuitable for anything past point-blank distance shooting.
In-game Description and Stats
"The Mars is a folding, concealable sub machine gun. It is employed by Federal Agencies such as the Secret Service and ATF."
Fire Rate: IIII
The Mars is based on the ARES FMG, a submachine gun that was designed as a personal defense weapon for VIPs and CEOs.
In The Omega Strain, it is bizarrely more powerful than the Stava M86, despite the fact that it fires 9mm rounds while the latter uses 5.56 NATO ammunition.
Despite being able to fold into a box in The Omega Strain, the weapon is always unfolded.