Visually, the weapon consists of a severed mantis foreleg, fitted to the wielder's forearm and reinforced with metal bars and leather straps. A handle on the "blade" allows stability. Although requiring a high Unarmed skill to use, it features a lackluster damage, though its quick attack rate somewhat makes up for the loss. It's selling point, however, is the critical multiplier of 3, allowing it to deal double damage more often.
Embrace of the Mantis King!Gun Runners' Arsenal, a unique variant evidently from the "Mantis King", that has greater damage but a slower attack.
The mantis gauntlet was to be a crafted weapon, similar to the deathclaw gauntlet from Fallout 3. Several resources, including an item called Schematics - Mantis Scythe point to this, though the inconsistency of the remaining resources as well as their only partial implementation make the specifics unclear.