Menacer
From Sega Retro
The Menacer is a light gun for the Mega Drive. The Menacer was compatible with either the 6-in-1 multicart which was packaged with the peripheral or Terminator 2: The arcade game. It uses an infrared receiver which is best positioned above the TV/monitor, and plugs into the controller port. It is similar to the Superscope for the SNES.
When fully assembled, it is more like a "light bazooka" than a normal light gun. The use it in this form, the user puts the Sega Menacer on his/her shoulder and uses the sight to aim. The shoulder rest and binocular scope are detachable, so the Menacer can be held like an ordinary pistol-like weapon.
The Menacer is incompatible with other games that require a lightgun - most notably, Lethal Enforcers, which requires Konami's own Justifier gun.