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For the monster spell that induces vulnerability, see Vulnerability (monster spell).

A vulnerability is a form of property in NetHack that signifies a weakness to certain types of damage, and is more emphasized in some variants of NetHack.


Monsters that have either fire resistance or cold resistance (but not both simultaneously) are considered vulnerable to the opposite element, and take about 57% more damage from rays of that element (+1d3 for each 1d6), as well as double damage from explosions of that element.[1][2][3] This is not applied to the player character, even if they polymorph into such a monster.


Elemental vulnerabilities are a significant influence on character builds and options thereof: one of the reasons Frost Brand is much preferred to Fire Brand is that a majority of late game monsters before the Astral Plane are vulnerable to cold, particularly the major demons, demon lords and princes in Gehennom.


Some variants expand on vulnerabilities to elemental damage, often incorporating additional weaknesses, and may introduce a means for monsters to induce vulnerability to elemental damage in your character or other monsters.


In EvilHack, certain monsters have vulnerabilities to specific types of elemental damage: these are handled via their own independent flags rather than in the code of applicable elemental attacks, including fire and cold vulnerabilities, so monsters may not possess the same vulnerabilities as they do in NetHack.

The vulnerability monster spell can be used by clerical casters of at least level 6, and causes an adjacent target monster (including you) to become more vulnerable to fire, cold, shock, or acid damage for several turns - the type of damage is chosen at random, and the spell suppresses any resistance the target has to that element for its duration. Kathryn the Ice Queen, Asmodeus and Vecna favor inflicting cold vulnerability with this spell, and will not inflict vulnerability to fire at all.


In Hack'EM, certain monsters have vulnerabilities to specific types of elemental damage as in EvilHack. The vulnerability monster spell is also available to clerical casters and functions the same.


  1. src/explode.c in NetHack 3.6.7, line 440: double damage from fire/cold explosions
  2. src/zap.c in NetHack 3.6.7, line 3629: extra damage from fire rays
  3. src/zap.c in NetHack 3.6.7, line 3649: extra damage from cold rays