Magic cancellation (3.4.3)

This page is for an older version of Nethack (3.4.3). For the current version see Magic cancellation.

For the effects of a wand of cancellation or a spell of cancellation, see Cancellation.

Magic cancellation, or MC for short, is a property of some pieces of armor which protects the player from certain non-damage effects caused by a monster attacking and touching the player with some part of its body. Examples include poison from killer bee stings, lycanthropy caused by werejackal bites, and the green slime's sliming attacks. Such attacks are referred to as special melee attacks in this article. A precise list of the special melee attacks that magic cancellation protects against is provided in the section below.

A player is protected from special melee attacks by an aura of magic cancellation if one of the pieces of armor worn has magic cancellation. Each piece of armor has a magic cancellation number (MC number) ranging from 0 to 3, where 0 is the lowest (worst) and 3 is the highest (best). Note that magic cancellation is not cumulative — the player's magic cancellation is the maximum of that provided by any single piece of armor worn. This means that if you are wearing a chain mail with MC 1, and a dwarvish cloak with MC 2, then your magic cancellation is 2. Having the highest (best) magic cancellation means that only 1/50 of special melee attacks will succeed (assuming they would hit otherwise). This makes magic cancellation a high priority trait.

Magic cancellation must not be confused with cancellation caused by a wand or spell, nor with magic resistance. See section Difference between magic cancellation, cancelling a monster, and magic resistance for further details.

What magic cancellation protects against

Understanding how magic cancellation works requires some understanding of how an attack works in NetHack. An attack has two characteristics: attack type (e.g. bites and stings) and damage type (e.g. physical or poisonous). A soldier ant for instance, has two attacks: a bite which does 2d4 physical damage (i.e. ordinary damage), and a sting which does 3d4 poison damage. Magic cancellation will not protect against the 2d4 physical damage from the bite, nor will it prevent the 3d4 damage caused by the sting. It will however protect against the special effects from the poisonous sting, which randomly includes hitpoint reduction, attribute reduction, and instadeath.

There is no obvious pattern to what magic cancellation does and doesn't protect against. Shortly put, magic cancellation protects against certain attack types that deal a certain type of damage. This relation is shown in the table below. To be prevented by magic cancellation, both the attack type and damage type must be in the orange area of the table. If either the attack type or damage type is outside the orange area, magic cancellation will have no effect on the attack.

In earlier versions of the game, the idea was that some types of armor covered your entire body surface, so the attacker effectively could not touch you despite his successful attack. Over time, with the addition of the cornuthaum and many types of special attacks, this point has become moot, and the current explanation can only be "it's magic".

Attack type		Damage type
Attack type unaffected	Attack type prevented	Damage type prevented	Damage type unaffected
Passive attacks Spitting attacks Engulfing attacks Breath attacks Explosions from proximity Explosions from dying Gaze attacks Magic spells Ranged weapon attacks	Claw Bite Kick Head butt Touch Sting Tentacle attack Holding attacks Melee weapon attacks	Fire (burns scrolls and boils potions) Cold (shatters potions) Shock (detonates rings and wands) Sleep (completely immobilized) Poison (hitpoint and attribute reduction, instadeath) Paralysis (player completely immobilized) Drain life (player loses levels) Sticky attack (inability to move to another square) Lycanthropy (player regularly changes form) Slowing attack (reduces player speed) Teleport (randomly teleports player) Sliming (kills player in a few turns) Disenchanting (reduces enchantment on items) Dexterity or constitution draining poison Power draining (reduces power)	Ordinary physical Magic missile Disintegration Acid Blinding Stunning Leg damage by Xans Petrification Gold stealing effects by leprechaun Item stealing Erosion (including rusting, corroding and rotting) Confusion Digestion Healing effects by nurses Drowning Intelligence drain Disease effect by Juiblex Seduction Hallucination Amulet stealing by the Wizard of Yendor Intrinsic-stealing by gremlins Random clerical spell, magic spellor breath weapon damage Special damage of the Riders
Examples — unaffected due to attack type	Examples — prevented due to combination of attack type and damage type.		Examples — unaffected due to damage type
Floating eye passive paralysis attack Disenchanter passive disenchanting attack Guardian naga spitting poison Ice vortex engulfing cold Red dragon fire breath Yellow light blinding explosion Medusa petrifying gaze Pyrolisk fire gaze Lich magic spells	Fire damage from a fire ant bite Cold damage from a lich touch Shock damage from an electric eel bite Sleep caused by a homunculus bite Poison damage from a killer bee sting Paralysis caused by a guardian naga bite Drain life by a barrow wight weapon attack Sticking-to caused by a large mimic bite Lycanthropy caused by werejackal bite when it is in animal form Slowing caused by the Shade touch Teleport caused by the quantum mechanic claw Sliming caused by the green slime touch Disenchanting by the disenchanter claw Constitution draining poison by the rabid rat bite Dexterity draining poison by the quasit claw		Physical damage due to tiger claws Medusa petrifying gaze Raven blinding claws Petrification (stoning) due to a cockatrice's touch or passive hissing attack Seduction due to succubus bites Intelligence drain due to mind flayer tentacle attacks Purple worm engulfing digestion Drowning due to giant eel wrapping Hallucination caused by a black light exploding Erosion due to brown pudding bites Nymph stealing claw

How the protection works

Magic cancellation protects the player by reducing the probability of special melee attacks occurring.

• The attack must first hit the player. This means passing the player's armor class. Unless you are resistant to the damage type of the attack, you will be dealt damage, which reduces your hitpoints. This occurs regardless of whether the damage type was ordinary physical, or a special type such as poison.
• After this, there is a probability of special effects occurring, for instance:
  • 100% Sticking-to, teleport, sliming, disenchanting, disease
  • 1/3 Drain level and paralysis
  • 1/4 Lycanthropy, slowing attack, and drain energy
  • 1/5 Sleep
  • 1/8 Poison
• Finally, the attack must pass the player's magic cancellation aura. The chance of this happening is listed in the table below:

Magic cancellation number	Chance of attack succeeding
Magic Cancellation 0	$\frac{150}{150}$, i.e. 100%
Magic Cancellation 1	$\frac{101}{150}$, i.e. ~67%
Magic Cancellation 2	$\frac{52}{150}$, i.e. ~35%
Magic Cancellation 3	$\frac{3}{150}$, i.e. 2%

If all these tests are passed, the player will suffer the special effect. In the case of fire, cold, and shock, there is further a test for determining if any inventory items are damaged or destroyed.

Magic cancellation is very useful, as can be seen from the following example. If you are wearing one of the best armors in the game, the gray dragon scale mail, you are are attacked by a vampire, then 1/3 of the vampire's successful bites cause you to lose a level. If however you wear an easy-to-find orcish cloak (MC 2) over the armor, the probability of the vampire's bites causing level drain will drop to $\frac{1}{3}\times\frac{52}{150}\approx 11.6\%$. An even better magic cancellation, such as that of an oilskin cloak (MC 3), would reduce the probability to $\frac{1}{3}\times\frac{3}{150}\approx 0.7 \%$.

Magic cancellation numbers of armors

All cloaks, some pieces of body armor, and the cornuthaum provide non-zero magic cancellation. All other items in the game provide zero magic cancellation. The following list contains all the pieces of armor with non-zero magic cancellation:

Armor name	Armor type	Magic cancellation number
alchemy smock	cloak	1
chain mail	body armor
mummy wrapping	cloak
orcish chain mail	body armor
orcish ring mail	body armor
leather cloak	cloak
splint mail	body armor
studded leather armor	body armor
cloak of displacement	cloak	2
cloak of invisibility	cloak
cornuthaum	helmet
crystal plate mail	body armor
dwarvish cloak	cloak
orcish cloak	cloak
plate mail	body armor
cloak of protection	cloak	3
cloak of magic resistance	cloak
dwarvish mithril-coat	body armor
elven cloak	cloak
elven mithril-coat	body armor
oilskin cloak	cloak
robe	cloak

Difference between magic cancellation, cancelling a monster, and magic resistance

Magic cancellation is a property of armor that reduces the probability of certain special monster melee attacks of succeeding. A monster can also be cancelled by zapping a wand or a spell of cancellation. This is somewhat different from magic cancellation. Cancelling a monster completely removes the monster's ability to perform its special melee attacks, while magic cancellation only reduces the probability of those attacks succeeding against the player. Also, the attacks affected by cancelling a monster are not exactly the same as those prevented through magic cancellation. See the article on cancellation to compare effects.

Magic cancellation is not the same as magic resistance. Magic resistance is an extrinsic that protects against spell, wand, and trap effects and damage. It is important to remember that cloaks of magic resistance also provide the highest level of magic cancellation.

Also note that the magical cancellation is different from intrinsic resistances against fire, cold, and shock damage. If you suffer fire damage while fire resistant, you won't be dealt hit point damage, but there is still a chance of items such as scrolls, spellbooks, and potions being destroyed. Magic cancellation on the other hand won't prevent the damage, but it will reduce the probability of item-destroying effects occurring.

Common misconceptions

• Magic cancellation does not protect against paralyzing passive attacks nor gaze attacks, which include the attacks of floating eyes and Medusa.
• Magic cancellation partially protects against disenchanters; it prevents the disenchantment though the claws, but not through the disenchanter's passive attack.
• Magic cancellation does not protect against the touch nor against the hissing attack of the cockatrice. It is however possible to cancel the cockatrice itself, using a wand of cancellation or spell of cancellation. This will remove its ability to petrify by hissing only.
• Monsters, including pets, enjoy magic cancellation from armor just as the player does. This is especially important if you rely on a powerful pet, as monsters cannot gain intrinsic resistances from eating corpses.

Strategy

Magic cancellation is a high priority trait, because it protects against many early game killers such as killer bees and soldier ants. Although orcish and dwarvish cloaks have no effect on AC, they both confer MC 2, which protects against roughly two thirds of special melee attacks. That makes them useful until mithril-coats and the rarer MC 3 cloaks are found. Most players strive to have maximum magic cancellation (MC 3), but some favour the benefits conferred by a cloak of displacement (MC 2) while wearing dragon scale mail (MC 0).

Variants

In Slash'EM Extended, a magic cancellation of 3 only prevents attacks 95% of the time instead of 98%.

References

• mhitu.c
• monattk.h
• monst.c
• mthrowu.c

External links

• armr-343.txt
• NAO top types of death