Roguelike column thumbnail ['@ Play' is a bi-weekly column by John Harris which discusses the history, present and future of the Roguelike dungeon exploring genre.]

/dev/null's annual Nethack tournament is, as I type this, winding its way towards concluding another successful year. While there have not been a good many surprises this time out (Christian "marvin" Bressler has already won Best of 13 again), there has been a fairly substantial surprise in the game itself.

One of the things that Nethack makes possible, and /dev/null takes advantage of in their contests, is for game administrators to provide customized games for their players. The level description files that Nethack uses to generate levels are separate from the game executable, and can be compiled separately from the main game without even invalidating old saves. The source code itself is also open, freely available on, which over the years has made possible Nethack's handful of variants, including Slash'EM. One might think that a game in which all its secrets are laid bare in the source code would provide no surprises for a player, and it is true that the source itself is the primary Nethack spoiler, but since the source is not always easy to read, and much of the game is randomly generated anyway, this doesn't tend to ruin the game. (In fact, if anything, only spoiled players ever seem to win at Nethack....)

So what /dev/null has done is implement a "challenge," a patch to the game that is added each year to the source of their version of the game to mix the game up for long-time players. (There is an option to play without it as well.) This was begun last year, with an appropriately far-reaching mood set by asking players to go over to popular webgame Kingdom of Loathing, which includes a special theme area as an homage to Nethack, and complete a quest there. This year's challenge is entirely in-game, adding new monsters and items and a special procedure to be undergone concerning them.

[Click through for more.]

Nethack patches are fairly numerous in general. Angband, Nethack's primary competitor for the position of most popular roguelike, is also open-source but its patchableness, combined with the relatively easy-to-understand code, has steered starry-eyed modders more towards the creation of new variants than just adding stuff to the core game. Nethack, on the other hand, has a notoriously twisty codebase with all kinds of gotchas waiting to pounce upon a untutored programmer, making the creation of full-fledged variants quite difficult for players without an encyclopedic knowledge of both the source and the C programming language, and its play has more unique character than Angband's anyway, so most patch authors content themselves with adding a minor feature or two.

Many of these patches can be obtained from the Nethack Patch Database, a website that catalogues and makes these source patches available for download. Compiling them into the game can be an adventure to itself, especially with some patches that have not been updated since older versions, but for those stout of heart enough to see them through their compilation are rewarded with some fairly radical changes to the play.

Among the the more promising patches out there, are:

Color Alchemy

A relatively recent addition to Nethack's formidable feature set is alchemy, which is implemented in the game by dipping one potion into another. It used to be that the result from such a combination was completely random, with a good chance of an explosion. More recently, a system has been implemented by which particular kinds of potions mixed into others would tend to make the same result. For example, mixing Healing and Gain Energy together yields Extra Healing.

The details of Nethack's alchemy system, as many other aspects of the game, can be learned at the Nethack Wiki, but that doesn't concern us at the moment. Color Alchemy discards that system entirely and replaces it with quite a nifty little idea: that mixing potions should produce results depending on the colors of the input potions more than their types.

Under the Color Alchemy patch, if you mix a potion of a red hue with a yellow one, the result will be orange. To elaborate: if you mix a potion type whose description is a red color with a potion type whose description is yellow, you will get out of it a potion whose description is orange.

This is a fairly ingenious change to the game. Under the old system, once you know what certain potions are, you can fairly consistently create certain other potions, but those mixtures do not change between games, and some of these potions, such as Full Healing and Gain Level, are highly desired. Since potion descriptions are randomized at the start of the game, playing with the Color Alchemy patch means entirely different combinations on every play. One game may have highly useful potion mixture combinations, another may have all valuable types combine to make crappy ones. It is possible for extremely useful mixtures to result from this, like two common potions mixing to produce Gain Level, but in the end the results balance out, since it would be fairly unlikely to happen, the player will have to have learned what the potions are to get real use out of this which implies the player has survived the early game, and in the long run level gain creates problems as it solves others, so it is a fairly well-thought-out change to the game.

Further, there is something intrinsically Nethackish about using a logical aspect of potion descriptions as the basis for mixing them. In a game where players can rustproof armor by reading a scroll of Enchant Armor while confused, color-based potion mixing fits right in. Because of this, this patch is considered by some to have a good chance of being incorporated into the next version of the game... but the ways of the Devteam are mysterious, and one can never speak for sure as to what they plan to do with the game in the next version.

Enhanced Artifacts

For all its wonders, there are also a fair number of head-scratching things about Nethack. One of the most scalp-tingling of these is the game's collection of practically-useless artifacts.

A Nethack artifact, to explain once more, is an unique, named object that carries special properties above the typical example of its class. Most of them are weapons, and some are quite nice to have in your hands. Many games have been won by players wielding the likes of Greyswandir or Excalibur. However, there are at least as many "useless" artifacts in the game, which few knowledgeable players would bother carrying around. Most of these are in a category termed the "Banes," a number of artifact weapons that grant attack bonuses against one class of monster and nothing else. Against monsters that are not dragons, Dragonbane is no different from an ordinary longsword. For a weapon of such superlative quality that only one of it exists in the world, this is something of a letdown.

Even this would not be so bad if the actual bonus was something so tremendous that it could, say, slay monsters of its class with a single blow, but this is not the case. One might think that a weapon whose specialty was the destruction of a particular species would at least be so powerful against it that it would be the obvious choice in such an encounter, but even against dragons, Dragonbane is nothing to write home about. Neither is Trollsbane all that useful against trolls, nor Werebane against lycanthropes, nor Ogresmasher against ogres. Bane longsword weapons, in particular, are outclassed against any foe by the headliners in that weapon category: Frost Brand, Excalibur, and Fire Brand. Even Vorpal Blade, which has a 5% chance of beheading foes but otherwise has a pitiful bonus, is better than Dragonbane. Further, most Banes can be made obsolete by a single blessed scroll of genocide, which may be rare but are far from unique.

What the Enhanced Artifacts patch does is take some of the less useful of these weapons and add extra powers to them. This usually takes the form of extra damage (especially in the case of Vorpal Blade and the Tsurugi of Muramasa), but the Bane weapons in particular have been focused on, granting them a substantial boost in to-hit and damage against their enemy races and giving them powers in addition to their normal weaponly function. Trollsbane grants regeneration and prevents trolls from coming back from the dead (again and again, dammit), while Dragonbane grants reflection, eliminating all threat from dragon breath and wand attacks at once.

The essence of game design is to provide the player interesting decisions to make, but a decision in which there are choices that are obviously good or bad is not a real decision. No player who knows what he is doing will choose Trollsbane over Frost Brand. Ultimately, what the Enhanced Artifacts patch really does is remove a little of the surety behind that decision, and that makes for a stronger game.


Nethack is a game known for the size of its bestiary. It contains hundreds of vicious foes, most of them with far more, um, personality than that of a garden-variety RPG. Nethack has monsters that quickly kill those unwise in dealing with them (giant eels), monsters that drain experience levels (vampires), monsters that cause amnesia (mind flayers), monsters whose corpses can be used as weapons themselves (cockatrices), monsters who can provide special armor (dragons), monsters who steal money (leprechauns) and items (nymphs), and even monsters who, properly approached, can help the player (succubi/incubi and nurses), and that's just scratching the surface.

But the thing about variety is, it never seems like there is quite enough of it. Even with all its wonders, there eventually comes a time in most players' hacking careers that the basic catalog of monsters begins to seem kind of boring. This is one of the primary reasons people play Slash'EM, the Nethack variant most likely to cause insanity: while Nethack merely appears to go overboard in every respect, Slash'EM truly does so.

But there is perhaps a middle ground between "considerably" and "absurdly" loaded with monsters, and that ground may well be occupied by the Biodiversity patch, which adds a number of new foes to the game, including one that fixes shoes, one that disintegrates objects with a touch, and even one that changes mazes. In a game that contains Keystone Kops (and used to have the Three Stooges) this may not seem like a big deal, but at least most of the added foes fall into the "monster has special unique powers" category, instead of the "monster has hit dice, three attacks and fire resistance" one, like, say, every monster in Angband.


One of the older modifications for the current version of the game is the Grudge Patch, which takes one of Nethack's central features, the core concept behind pets and rings of conflict, the idea that monsters can sometimes hit other monsters instead of the player, and runs with it. Simply, Grudge gives certain monsters a greater priority in their lives than killing that particular @-symbol who happens to be traipsing through the maze at that moment. All you people who sat and thought unkind things about a game in which elves happily attack the player alongside orcs, your nerdly objection has been heard!

Pet Ranged Attack

The thing that most people know about Nethack, if they know anything about it at all, is that players begin with a pet, a little dog or a kitten (or sometimes, in recent versions, a pony). This pet will often not last long in the dungeon, but that's okay as a canny player can acquire a new one, can in fact build an army of loyal lackeys to tackle the dungeon for him.

A pet is a monster that fights for, rather than against, the player. But there are more differences than that. Pets can steal from shops, provide hints as to what is safe to eat, and help identify cursed objects. Pets can also grow hungry over time, which untamed monsters do not, and the player is punished, sometimes harshly, for not treating his minions with the proper respect.

Many Nethack patches, as we have seen, get their inspiration from fixing some of what are perceived as the more lacking aspects of the game. One can't help but think each of them occurred because the patch author once had a game in which he was bitten by the lack of the expected behavior. The oversight the Pet Ranged Attack patch corrects is the fact that, when a monster becomes tamed by the player, it seems to suddenly forget how to fire missile weapons, use its breath weapons or cast magic. The great majority of Nethack's non-human monsters can be tamed, but this situational memory condition makes some of the most powerful of the lot, liches and dragons in particular, tragically ineffectual once they start working for the player.

When playing a game with the Pet Ranged Attack patch applied, pets will attempt to use distance attacks, including beam-attacks like rays and breath, against the player's foes. They will even make an effort not to harm the player with these blasts. However, since ray attacks may carom off walls and sometimes take random bounces, one should keep in mind that having a pet Black Dragon while not having a reflective shield, amulet or suit of armor is a recipe for disaster.

New Bigrooms, New Castles, New Medusa Lairs, New Sokoban Levels

Bigrooms occur on a certain range of levels, relatively early in the dungeon, and are, as the name implies, made of one gigantic room without things like sight barriers or corridors to impede the monsters from merrily sidling up next to you and whacking you to the extend of their joyous monster heart's desire. Nethack Bigrooms are implemented as semi-hardcoded levels with predefined layouts and some randomized aspects, such as monster types and stair locations. When one appears (only in a small percentage of games), it is chosen from one of a number of pre-made layouts, but they are all generally wide-open and easy to get surrounded in.

The Castle appears fairly deep underground, and mark the transition between the Dungeons of Doom and Gehennom, the two major halves of the game. Like Bigrooms, it is semi-hard-coded, although there is only one main Castle layout in basic Nethack. It always contains a drawbridge, pits leading to the next level instead of stairs, and a certain very powerful aid to the player's quest. It also has many particularly tough monsters, and it serves as the last major trial before the player can seriously undertake the search for the Amulet of Yendor.

The Medusa level is a few floors up from the Castle, and since it is mostly flooded the player usually needs a means of crossing water to proceed. There are two potential layouts to the Medusa level, but both of them have the gal herself standing on the downstairs, and special measures must be taken to prevent turning into a statue at the mere sight of her.

Sokoban is a dungeon branch relatively early in the game, accessed from a second set of up stairs found shortly after the Oracle level. Unlike most branches it leads up, not down, and always contains four levels. Sokoban levels are a bit less random than most, and contain a pre-written arrangement of boulders and pits. The level also has special rules patterned after its namesake game, which prevent boulders from being pushed diagonally, or getting past a pit unless it has been filled. Sokoban's layouts, consisting as they are of traditional box-pushing puzzles, are all pre-written, and each floor, of ascending difficulty, is chosen from one of two alternatives when it is first entered.

As for the patches themselves? They simply increase the number of possible layouts for these levels. The Sokoban patch is interesting since it adds 19 more possible puzzles to the 8 included in the game. The Castle patch adds variety to a level that formerly had fairly little, since in vanilla Nethack there is only one Castle layout.


Excluding branches, there are three major sections of Nethack's dungeon. The one most players are familiar with is the Dungeons of Doom, which goes from the surface down to the Castle. Above the upstairs are the Planes, which make up the endgame and can only be accessed once the player has the Amulet of Yendor. After the Dungeons and before the Planes is Gehennom, which goes from the Valley of the Dead down to the bottom-most level, where the Amulet is kept.

The Dungeons of Doom are composed of rooms and connecting passages drawn between them. Gehennom, in contrast, is made up of a good number of mazes, with the occasional special level thrown in.

These mazes comprise that many consider to be the most boring portion of the game. A player who has reached them has probably cleared the Castle so he is not likely to be overwhelmed by monsters at this point, and the demons that infest Gehennom, while strong, are not much stronger than some of the monsters the player has likely already faced, like xorns and liches. Notably, most of the demon lords and princes in Gehennom are relative pushovers for an even slightly-prepared player. There is still the Wizard of Yendor to contend with, but it's some time before he shows up.

Meanwhile, as I said, most of these levels are mazes, and it usually takes much longer to explore a maze than a complex of rooms, while being less interesting to explore. There are no special rooms in the mazes, nor any altars, fountains or sinks. The stairs down might be two spaces away from the entrance, or they might be clear on the other side of the level. Along the way there is the usual mix of increasingly-pathetic monsters to slay, which becomes more and more just a formality as the player continues into the depths.

I explained a month ago that it is possible to teleport down many levels at once if the player is suitably prepared, yet the player cannot really skip the mazes: once the Amulet is obtained the player must escape with it, and player-initiated level teleport does not work while it is carried. It must be brought, from the lowest level, all the way back up to the top of the dungeon on foot, with the occasional random teleport down a few floors just to be frustrating, so a smart player has planned for this by mapping out all the levels ahead of time. This makes the formerly-useless scrolls of magic mapping nearly essential on the way back out of the dungeon. It also makes for a fairly tedious experience, as all those mazes do not have much variety to recommend them.

A number of patches have been created to address this perceived failing of the game. Slash'EM handles it by cutting out the mazes almost entirely, increasing the size of the main dungeon and making Gehennom more of a collection of special levels than a huge maze. It also gives all the unique demons their own special level, including rarely-seen special guest star Demogorgon, the deadliest monster in the game. The Lethe patch makes Gehennom more perilous by introducing rivers of amnesia-inducing water, as well as throwing in more special levels, many of them populated with a selection of Lovecraftian monsters.

HeckĀ²'s solution to the problem is not to make Gehennom shorter, but to make it more interesting by throwing more special levels in to the mix. It comprises 42 special levels that can replace a substantial portion of Genhennom's random mazes. Some of the random possibilities include special levels for the guest demons, but there are plenty of other interesting possibilities, such as a one containing a small coven of amnesia-causing mind flayers, and a maze made up of Nethack's least-known terrain type, iron bars, which can be seen through but not passed.

While Nethack is open source, its official maintainers are not promiscuous about the contributions they accept. For all out patch inclusiveness there is Slash'EM, a game that contains automatic weapons (as in, machine guns), lightsabers, doppelgangers and vampires as a player races, special character abilities (some of which, it must be said, are incredibly geeky, like the Monk's Final Fantasy VI-inspired direction inputs to execute special moves) a load of new character classes and a couple additional legs to the main quest, among other additions. While it is at times disappointing that the Devteam seems to have become fairly conservative, not to mention slow, concerning the things they add to the game, for players who wish more there is always Slash'EM. And for those who would like to retain at least a few of their sanity points, there is the world of user-made patches.