Rust monster

R rust monster
Difficulty	8
Attacks	0d0 touch rust, 0d0 touch rust, 0d0 passive rust

R rust monster
Difficulty	8
Attacks	0d0 touch rust, 0d0 touch rust, 0d0 passive rust
Base level	5
Base experience	70
Speed	18
Base AC	2
Base MR	0
Alignment	0 (neutral)
Frequency (by normal means)	2 (Quite rare)
Genocidable	Yes
Weight	1000
Nutritional value	250
Size	Medium
Resistances	None
Resistances conveyed	None
A rust monster: can swim. has no hands. is an animal. can eat metal. is normally generated hostile. can be seen through infravision.
Reference	monst.c#line1869

A rust monster, R, is a type of monster that appears in NetHack. It is one of the two members of the rust monster or disenchanter monster class.

Rust monsters are metallivores that are capable of swimming, but unlike other metallivores they will only eat rustable metallic items they come across - they will avoid eating other non-rustable metals, as well as the amulet of strangulation and the ring of slow digestion (if the ring's randomized appearance is metallic). A rust monster has two touch attacks and a passive attack that deal no direct damage, but instead rust worn metallic armor, with the passive rusting metallic weapons used to hit them; both attacks have no effect on erosion-proofed armor and weapons.

A rust monster that eats a metallic item restores its HP up to an amount equal to that object's weight; if a rust monster attempts to eat something rustproofed, it will instead spit it out, removing the proofing and leaving it stuned, which also applies to you if you are polymorphed into a rust monster. Tame rust monsters consider rustable iron-based items to be treats.

Generation

Rust monsters often begin randomly generating midway through the dungeon. The random R placed in the throne room of the Castle on level creation is likely to be a rust monster.

Strategy

Rust monsters are a common mid-game annoyance for players: their speed of 18 makes evasion and maintaining distance difficult, and their passive rusting reduces the amount of viable options for ranged attacks that can keep them from compromising metal armor. Fortunately, rust monsters have no monster MR, leaving them very vulnerable to wands and spells. Standard unarmored pets such as cats and dogs can more easily deal with them without fearing retaliation.

Wearing non-metal armor or rustproofing whatever metal armor and weapons you have will render rust monster attacks completely harmless. For players who lack the means to do so, unicorn horns are a solid backup weapon to use when fighting rust monsters, and Elbereth can push rust monsters back out of melee range, providing time and space to either fire wands and spells at them or else to remove any metallic armor before engaging in melee.

Even after they are no longer a danger to your own inventory, rust monsters remain an annoyance due to their tendency to eat any metallic loot lying around, often before you can get to it - this is especially undesirable on a level with bones and/or any metallic artifacts, though artifacts will resist being eaten or rusted 95% of the time.

Like other metallivores, rust monsters can be used to deal with punishment in some cases by having them eat the iron ball and chain attached to you, though they will usually try to rust your armor afterward unless a tame or peaceful one is used.

As pets

While generally unremarkable as pets, tame rust monsters are very easily fed if you do not care about picking up any further metallic items. Be sure not to throw iron projectiles or other weapons directly at a pet rust monster!

History

Rust monsters have been present in the game since the PDP-11 variant of Jay Fenlason's Hack; hack121 instead has the oxidizer, which serves roughly the same role. From this version to NetHack 3.0.10, including variants based on these versions, rustable weapons and armor that were subjected to erosion instead had their enchantment reduced; rust monster attacks could bring enchantments as low as -2 with their attacks, making them somewhat similar to modern disenchanters. Proper object erosion was introduced in NetHack 3.1.0.

Origin

The rust monster is one of many NetHack creatures that comes from Dungeons & Dragons, first appearing in the 1975 Greyhawk supplement for the original release. The rust monster and several other creatures in particular were based on dime-store plastic toys that were used by Gary Gygax and other play-testers as monster figures, with their appearances based directly on the toys.

A rust monster is a pony-sized creature that dwells underground, with a squat and humped body, four insectoid legs and thick, lumpy hide. It can smell metal from up to ninety feet away, and the long antennae that extends from under each of its eyes can instantly rust or corrode any metal they touch to the point of falling apart—its hide has the same effect on weapons that strike it, and magic items weapons have a chance of resisting proportional to their enchantment. A rust monster's diet consists of freshly-rusted ferrous metals such as iron, steel, and steel alloys, which it prefers to other metals; adventurers can take advantage of this by distracting it with suitable throwaway items.

Messages

<The rust monster> spits <foo> out in disgust!

A rust monster tried to eat an item that was rustproofed, stunning it and removing the proofing.

Ulch - that <foo> was rustproofed!

You were in the form of a rust monster and attempted to eat a rustproof item; this is followed by one of the two messages immediately below.

You spit out <foo> onto the <surface>.

You spit out a rustproofed item that you attempted to eat while in the form of a rust monster, dropping it onto the ground.

You spit out <foo>.

As above, but the item is cursed and remains welded to you.

Encyclopedia entry

These strange creatures live on a diet of metals. They can turn a suit of armor into so much useless rusted scrap in no time at all.