The dragons, represented by the overall glyph D, are a class of very powerful mid-game monster in NetHack and 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. (Note that dragon corpses are very filling so using a tinning kit is often a good idea.) Dragons will always leave corpses, and have a 1 in 3 chance of also dropping scales (1 in 20 if the dragon was revived). Baby dragon corpses do not grant intrinsics, nor do they drop scales.
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, at Fort Ludios, and they are randomly generated at rather deep dungeon levels by normal random monster generation, on the healer quest, or 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||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 a reliable defense against the black dragon's disintegration blasts. (The only other disintegration is wide-angle disintegration beams from angry gods, which can't be reflected.)
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 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 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 in any of the dragon 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 color for dragons are Silver and Grey; they are immune to death rays and the former is also immune to disintegration, while the latter is immune to levelport and polymorph traps. Yellow is a good option too due to being stoning-resistant.
In SLASH'EM, the Hydra and wyvern monsters also use the D glyph. SLASH'EM also added two new dragons, The Shimmering D and Deep D variants. Baby dragons have a base level of 4 instead of 12, and adult dragons have a base level of 18 instead of 15. Also, baby dragons can be randomly generated on all levels, even in places in Nethack that normally had guaranteed adult dragons, such as Fort Ludios or The Castle. As a result of the changed monster polymorph rules, increased difficulty of adult dragons, removal of most guaranteed adult dragons, and increased level difference between adult and baby forms, dragon scale mail is significantly harder to come across in SLASH'EM without using reverse genocide or a wish.
Interestingly, blue, black, white, red, and orange dragons have a chance of turning traitor, while gray, silver, green, and yellow do not.
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."
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.