Portable Guillotine (3.5e Equipment)
From D&D Wiki
The portable guillotine created by mounting a set of 4 - 6 large blades onto hinges in the bottom of a small bird cage. The cage then has a long chain attached to it(usually about 45 feet) for throwing onto enemies. The cage is thrown onto the head of an enemy, and then the chain is given a strong pull which forces the blades to close around the victim's neck. A sufficiently strong pull of the chain causes the blades to go right through the neck and decapitate the victim.
The weapon can only be used effectively if the user is at least 5 feet above the person he is trying to attack(less than that and the attacker takes a minus 4 to the attack roll). The guillotine is purchased by what size creature it can be used to attack. The guillotine can be used to attack a creature one size larger or smaller than the size of the guillotine(i.e. a medium guillotine can be used on a small, medium, or large creature) but with a penalty of -4 to a creature larger than the guillotine's standard size.
 Mechanics of use
The user must make and ordinary ranged attack roll. With a successful attack the victim is given an opportunity to make a reflex save(assuming the victim is not flat footed) with a DC equal to the attack roll. The attacker must then make an opposing strength check with the victim to inflict damage. A success on the victims part of of 10 or more removes the guillotine entirely and has a 10% chance of pulling the attack down from his high point, a success of more than 5 reduces the damage to 0, and a success of less than 5 reduces the damage by 1 half. A success on the attacker's strength check of less than 5 deals damage normally, a success greater than 5 doubles the damage, and a success of 10 or more decapitates the victim.
While a creature has a portable guillotine on their head that creature loses their dexterity modifier to their AC, and is considered flanked.
 Society's View
Portable guillotines are difficult to find in a civil society, and are rarely sold openly. Most 'good' people view the weapon as both cruel and incredibly violent. Generally a character must special order one through less than reputable sources. It is, however, not impossible to find and can be quite effective in the hands of a character who has had proper training with the weapon( Favored Weapon(Portable Guillotine) etc...).