The dragons, represented by the overall glyph D, are a class of very powerful mid-game monster and are coveted for the scales they sometimes drop. With some superficial differences, they are nearly identical. Each of them has a nasty breath associated with their resistance. There are also baby dragons, which do not have a breath attack. Baby dragons randomly occur only on those levels that are eligible for baby monsters; otherwise they can be created by hatching from eggs.
Each dragon has a specific resistance associated with it. Eating some dragon corpses can give you the associated intrinsics; others can give you the extrinsic ability by enchanting their scales to make dragon scale mail. (Dragon corpses are very filling, so using a tinning kit is mostly a good idea. Be aware that tinning still won't work on half eaten corpses and at least for lawfuls eating after being satiated abuses your wisdom.) Dragons will always leave corpses, and they have a 1 in 3 chance of also dropping scales (1 in 20 if the dragon was revived). Baby dragons do not drop scales, nor do their corpses grant intrinsics.
A shimmering dragon, whose scales grant displacement, appears in the code, but is commented out by default, because monster displacement has not yet been implemented in vanilla NetHack. However, these creatures do appear in SLASH'EM.
Dragons are guaranteed on the Castle level and at Fort Ludios. They can be randomly generated by normal random monster generation at rather deep dungeon levels, on the healer quest, and in throne rooms. Other powerful monsters may generate them with the summon nasties spell.
Breath weapons and resistances
|Dragon||Breath (4d6 unless otherwise noted)||Intrinsics/scales||Corpse conveys...|
|Blue||lightning||shock resistance||same (100%)|
|Black||disintegration||disintegration resistance||same (100%)|
|Gray||magic missile||magic resistance||nothing (magic resistance cannot be gained intrinsically)|
|Green||poison||poison resistance||same (100%)|
|Orange||sleep, 4d25 turns||sleep resistance||same (100%)|
|Red||fire 6d6||fire resistance||same (100%)|
|Silver||cold||reflection and cold resistance; only reflection is provided by scales||nothing (reflection cannot be gained intrinsically)|
|White||cold||cold resistance||same (100%)|
|Yellow||acid||acid resistance and petrification resistance; only acid resistance is provided by scales||nothing (neither resistance can be gained intrinsically)|
A black dragon is the only source of disintegration resistance in the game; this might make acquiring disintegration resistance tricky were it not for the fact that reflection is already a reliable defense against the black dragon's disintegration blasts. (The only other disintegration is wide-angle disintegration beams from angry gods, which can be survived only by being resistant or sensible regarding religion.)
- a shield if worn, otherwise:
- body armor if worn (plus any cloak), otherwise:
- an amulet of life saving if worn,  otherwise:
The rebound can still kill you/it in case your gear saved you from the direct hit.
A gray dragon (or baby gray dragon) is often the eventual result of repeatedly displacing your pet onto a polymorph trap, because it is magic resistant, and hence will polymorph no further. However, it can still polymorph if it eats a chameleon or doppelganger corpse.
Dragons will use their breath weapons only at range (i.e. more than one square from the character), meaning that if you can get close to within melee distance, you can avoid the dangerous attacks in favour of the relative "safety" of their physical melee attacks. This is useful for characters without magic cancellation, magic resistance, or reflection to avoid or negate their elemental fire, cold, lightning, poison, or disintegration beams.
Dragons are excellent pets in the early game if you ever get one. The easiest way to get a dragon pet is through a dragon egg; the egg may be obtained by polymorphing into any of the dragons and then sitting if your character is female. If you repeatedly displace your pet onto a polymorph trap you will often end up with a gray dragon, since they are magic-resistant and will not polymorph further.
The most recommendable colors for dragons are silver and gray; they are immune to death rays and silver ones also immune to disintegration, while gray ones are immune to polymorph traps. Yellow is a good option too due to stoning-resistance.
Pet dragons can be used as steeds with the advantages of flight, fighting strength, and carnivorousness, which makes them easy to feed. However, they are quite slow and will spend most of their time either catching up with you or eating corpses unless you make them fast (eg by zapping a wand of speed monster at them).
Baby dragons generally possess the resistances of their adult forms. However, baby silver dragons do not possess reflection. They grant no intrinsics when eaten, they do not drop scales, and they do not have breath attacks.
However, one can still use tame baby dragons to obtain scales and/or resistances. Pet baby dragons will eventually grow up into their adult forms, which can then be killed (possibly via conflict or by rendering them non-tame through abuse) for their scales and intrinsics. Obtaining pet baby dragons can be accomplished via controlled polymorph for a female character fairly easily: all dragons are oviparous, and baby dragons coming from laid eggs will be tame. A male character can use an amulet of change to swap genders, or he can repeatedly polymorph into a dragon using the spell or the ring until he changes sex.
Dragons have been substantially modified in UnNetHack. All dragons have been given new names and have their breaths, resistances, and colors randomized, with the exception of chromatic dragons, which possess all breaths, and all resistances except for magic resistance. As result it is impossible to predict breath type based on name or color. This behavior has been made a bit more friendly in the current version - dragons are randomized at the start of the game, but all dragons of the same name/color are of the same type - identify one, identify all of that type. They auto-identify upon witnessing the breath attack. In addition, a new type of breath attack has been added - a lava breath that does heavy fire damage and melts walls instead of bouncing.
Glowing dragon scales and scale mail function as an infinite light source, in addition to providing the resistance that glowing dragons possess in each individual game. Chromatic dragon scales and scale mail provide all resistances (including reflection) except magic resistance.
The following are the names given to random dragons in Unnethack:
- glowing dragon
Hack 1.0 has a dragon that does not have an explicit color. This early dragon breathes fire and its corpse confers fire resistance, making it equivalent to the modern red dragon. Back then, it was the only way to get intrinsic fire resistance, so it was quite likely that the player wouldn't have acquired it yet by the time they would see dragons. This, combined with the lack of reflection and fact that in earlier versions of NetHack, dragons were allowed to use their breath attack in melee (on top of their normal melee attacks), made them significantly more dangerous.
NetHack 2.3e introduces all of the modern dragon types except silver. The corpse is still just a "dead dragon", without reference to the color, and eating it confers fire resistance, regardless of the type of dragon. Black dragon breath causes instadeath, and there is no reflection, disintegration resistance, or amulet of life saving, making genocide tempting; but fire resistance is necessary to enter Hell, and there's no way to genocide only black dragons.
NetHack 3.0.0 introduces baby dragons, makes the corpses separate, and also introduces dragon scale mail. Dragon scale mail is obtained by polymorphing a dragon corpse. Reflection is now available and black dragon breath is toned down a bit. It also becomes possible to genocide only black dragons.
NetHack 3.1.0 introduces dragon scales and with them the modern method of obtaining dragon scale mail. This version also adds the Quests and with them the Chromatic Dragon and Ixoth. Fire resistance is not necessary to enter Gehennom.
NetHack 3.3.0 adds the silver dragon and corresponding scales.
In the West the dragon was the natural enemy of man. Although
preferring to live in bleak and desolate regions, whenever it
was seen among men it left in its wake a trail of destruction
and disease. Yet any attempt to slay this beast was a perilous
undertaking. For the dragon's assailant had to contend
not only with clouds of sulphurous fumes pouring from its fire
breathing nostrils, but also with the thrashings of its tail,
the most deadly part of its serpent-like body.
"One whom the dragons will speak with," he said, "that is a
dragonlord, or at least that is the center of the matter. It's
not a trick of mastering the dragons, as most people think.
Dragons have no masters. The question is always the same, with
a dragon: will he talk to you or will he eat you? If you can
count upon his doing the former, and not doing the latter, why
then you're a dragonlord."
- courmon in mkroom.c
- zap.c in NetHack 3.4.3, line 3120
- zap.c in NetHack 3.4.3, line 2981
- Corner case: an amulet of life saving is never destroyed by the blast, but it does not die instead of an undead or non-living monster. This can only arise if a living monster wearing an amulet is subsequently polymorphed.
- muse.c in NetHack 3.4.3, line 2058
- polyself.c in NetHack 3.4.3, line 488