Beheading and bisection

Beheading and bisection are properties that appear in NetHack. Both are defined in the code of artifact.h by the same flag, SPFX_BEHEAD, and are properly distinguished from each other through code in artifact.c.

Description

Beheading is associated with the one-handed artifact weapon Vorpal Blade, while bisection is tied to the two-handed Tsurugi of Muramasa. Both have a 5% chance to occur when a monster (including you) is hit with either weapon, and deals HP damage equal to twice their maximum HP; though in practice it immediately kills the monster, this is technically not considered an instadeath due to how damage is calculated.

You cannot behead or bisect yourself by throwing either weapon in the air using <, and will only take normal damage from the weapon falling back down and hitting you.

Beheading

A monster that has a head is vulnerable to being decapitated by Vorpal Blade; a player polymorphed into a monster that is decapitated will die and be returned to their base form as usual. If Vorpal Blade hits a jabberwock (including a player in the form of one), it will always behead them. As implied by a comment elsewhere in the code, how many heads the monster actually has (e.g. ettins and their zombie/mummy forms) has no bearing on the beheading effect: so long as it meets the above conditions, Vorpal Blade can behead and kill it.

This chance is still accounted for if the target monster has a headless form or is currently engulfing you: the sword instead has a 5% chance of dealing no damage in those cases, as the blow will "miss <foo> wildly". If you would behead a monster with Vorpal Blade and the target has a head but is unsolid, the sword will slice through its neck without beheading them, which is treated as a normal hit.

Despite its name, the deferred monster known as the vorpal jabberwock does not have any beheading attacks, and is simply a tougher jabberwock.

Bisection

When a monster (including you) is hit with The Tsurugi of Muramasa, it has a 5% chance to bisect and instantly kill that monster if they are medium-size or smaller, while a monster that is large or bigger takes double damage. If you use the Tsurugi hit a monster engulfing you and bisection occurs, the engulfing monster will be instantly killed regardless of size.

Unlike Vorpal Blade, size is the only attribute of a monster that is accounted for when determining if bisection occurs or not - unsolid and corporeal targets alike will be slashed in half if they are small enough, or hit for double damage if big enough.

Variants

Both Vorpal Blade and the Tsurugi of Muramasa retain their beheading and bisection properties in variants of NetHack. In addition, some variants have a vorpal object property that is rarely found on some weapons, and uses the that is rarely encountered in some variants.

Most variants that implement the vorpal jabberwock often give its claw attacks the ability to behead monsters that it hits, and also make it so that Vorpal Blade always decapitates them as with normal jabberwocks.

SLASH'EM

In SLASH'EM, Vorpal Blade beheads foes 10% of the time instead of 5%, making it considerably more powerful. A similar weapon, Thiefbane, has a 10% chance of beheading any @. The vorpal jabberwock will not be instantly beheaded by Vorpal Blade, and has the same 10% chance as any other monster.

The potion of invulnerability does not protect you from beheading, since it only prevents standard HP loss.

GruntHack

GruntHack has the "vorpal" object property, which can only occur with bladed weapons. Single-handed weapons with the vorpal property function the same as Vorpal Blade, beheading solid non-headless targets with a 5% chance and always beheading jabberwocks. A two-handed vorpal weapon will instead bisect enemies as The Tsurugi of Muramasa does, with a 5% chance of instakilling small creatures or of cutting deeply into large creatures.

GruntHack also implements the vorpal jabberwock and gives this property to its two claw attacks.

UnNetHack

UnNetHack makes use of the vorpal jabberwock and gives its claw attacks the ability to behead targets, though the chance is halved to 2.5%.

dNetHack

dNetHack also has the vorpal object property, though it functions differently: the vorpal type is chosen based on the object's damage types, and vorpal weapons that are both slashing and piercing will decapitate the target. The chance of decapitation is 5%, as in vanilla NetHack; decapitation will also damage and potentially destroy that monster's helm, based on its AC value (and regardless of whether or not that helm would actually be caught in a beheading blow).

In addition, dNetHack introduces several new artifacts capable of decapitation:

• Release from Care and Crescent Blade can behead their targets, with the same chance as Vorpal Blade.
• The Lifehunt Scythe will only behead targets while sneak-attacking with it, with the normal 5% chance per hit.
• The Dragon's Heart-Stone can behead monsters that are not aware of your location.
• Snickersnee and The Kusanagi no Tsurugi are capable of beheading monsters.
• Levistus's Shadowlock can behead its target.

DynaHack and FIQHack

In DynaHack, the vorpal property functions the same as in GruntHack, except that it no longer occurs on randomly generated objects. The same is true in FIQHack.

EvilHack

In EvilHack, Cerberus is made immune to instadeath in this manner: if beheaded, he will instantly grow a new head in its place before the other two can be removed. EvilHack also uses the deferred vorpal jabberwock, which has decapitating claw attacks and behaves very similarly to GruntHack's version of the monster.