ArmsCor (an abbreviation for the Armaments Corporation) is a South African weapons company, whose most notable weapon is a 12-shot MGL. However, Incognito's seems to be modified and only holds 8.
The grenade launcher is attached to his arm, supported by chains that wrap around his torso. He is able to produce this weapon from his arm at will, ejecting it from his flesh when he needs to use it.
The Multiple Grenade Launcher's cartridges are filled with powerful, red, helical spines which are powered with dark magic and resemble DNA chains. When the launcher is fired, the cartridge shatters, launching the spines in a manner similar to a shotgun. While the effect these have on a human target is never shown in the Anime, they appear to be powerful enough to be of note to Alucard. When reloading is required, Incognito vomits green slime, which congeals into a set of dark magic spins into the cartridge assembly of the gun.
This weapon is first used against Alucard (who identified it by name) in Episode 9; after the powerful vampire asks what Incognito has done (to his master Integra), Incognito shoots him and the spines go through his chest, causing him noticeable pain. The weapon is later used against Alucard again in their confrontation in Episode 12, where the spines slash up Alucard's face and damage his body; and again in Episode 13, where Alucard (in his Level 1 form) dodges the spines. When Incognito is seen impaled at the end of the episode, the MGL is still hanging front his arm by its chains.