Disenchanters are considered to be rather annoying - their sole attack does a decent amount of damage, but more worryingly can decrease the positive enchantment of its target's worn armor. In addition, weapons and other items used to attack a disenchanter in melee may also have their positive enchantments or charges reduced. Artifacts have a 90% chance of resisting.
Disenchanters are a nightmare to face in close combat due to their very good AC of -10. The disenchanting claw attack is subject to magic cancellation; having MC3 through a cloak of protection or other means will reduce the enchantment you lose from your armor, but does not prevent the passive disenchanting attack. However, disenchanters have 0 MR, leaving them completely vulnerable to magical effects such as polymorph, cancellation, and sleep, and they can be easily warded off using instruments such as a tooled horn or leather drum to scare them. Attack spells and wands can keep them at bay with far less risk to your armor, though their AC will make landing shots a significant problem.
The "simplest" method of killing a disenchanter is to solely use unenchanted weapons such as weapon-tools like pick-axes or unicorn horns, unless you are actively using them as your main weapon; secondary starting weapons that went mostly unused may also prove a viable backup if you kept them around. If you have immobilized a disenchanter, or else armor enchantment is not a pressing issue for you, you can also remove your gloves to preserve their enchantment and bash it to death with your bare hands. (Monks aiming to kick one to death will also want to mind the enchantment of their boots). Similarly, strong pets that do not rely on weapons or else are wielding unenchanted ones will have no trouble against them.
Disenchanters are often a common target for single-species genocide, as rust monsters are not much of a threat once the player reaches Gehennom. However, they can also be useful to roles who cannot reliably cast drain life, providing an alternate method to selectively reduce the enchantment on a wielded weapon or piece of armor so it can be re-enchanted to a higher level. If you try this with your cloak, be sure to have a substitute for MC3 in order to nullify its attack.
The disenchanter is a monster that originates in Dungeons & Dragons, making its debut in the 1st edition Fiend Folio and issue #6 of White Dwarf. It is often described as a blue-furred quadrupedal creature with an elephant-like trunk and a camel-esque body and "hump". Disenchanters are considered even more infamous in tabletop settings, not solely for their magic-eating abilities, but also for their somewhat goofy-looking designs.
The disenchanter was added in NetHack 3.3.0.
In SLASH'EM, disenchanter corpses are safe to eat. Additionally, they are no longer the only monster that can disenchant weapons and armor with the addition of the steel golem, which has also a passive disenchanting attack.
In UnNetHack, eating a disenchanter corpse has a 50% chance of removing a random intrinsic, in a way similar to being hit by a gremlin at night. While potentially dangerous, this could also potentially be used to get rid of harmful intrinsics gained accidentally.
Ask not, what your magic can do to it. Ask what it can do
to your magic.