When hallucinating, randomize dragons’ colors and glyphs among all dragon colors/glyphs, and allow messages about them to use hallucinatory colors, e.g. “The mottled dragon bites!”
In the owned artifacts patch, wishing for dragon scales or scale mail may instead spawn a dragon of the requested color, who is still wearing the scales.
Mithril dragon, a dragon which spawns only if you (or possibly any creature on the level) is carrying over 75 aum of mithril in open inventory. It eats mithril items (and only mithril items, rather than being generally metallivorous).
Rust dragon, a type of dragon which breathes and makes melee rust attacks. It eats all types of metals. As with other metallic dragons, it is lawful.
Chaos dragon: a dragon with polymorphing breath, and whose scales grant unchanging. The dragon also has unchanging naturally (which raises the question of what happens if you polymorph into it, then die).
Polymorphing a dragon corpse creates a random object made of dragonhide.
Dragonbane starts off as just a weapon with a damage bonus versus dragons, but it gains properties corresponding to every type of adult dragon you have killed with it. So when you kill a red dragon with it, it now gives you fire resistance and/or does fire damage, then you kill a black dragon and it now gives you fire and disintegration resistance and/or does fire and disintegration damage, and so on.
This doesn’t have to be Dragonbane, the concept of an artifact that powers up by killing different monsters could apply to something else, but Dragonbane is a good example since dragons have a big diversity of obvious properties and resistances.
To keep it from becoming overpowered, it could stack up to 2 or 3 properties from the last 2 or 3 unique types of dragons killed so long as neither property is something powerful like reflection or magic resistance (which would clear all other properties).
Pet dragons that eat mimic corpses should turn into large piles of gold, consistent with the stated reason that pets tend to mimic things they are thinking about.
Dragonhide bags of tricks only spawn dragons. (Though this would include baby dragons, so it would probably at least approximate being level-appropriate).
“Dragon hoard” themed room: containing a big pile of gold scattered within a radius of 2-3 tiles around its center point, with larger stacks of gold closer to the center of the pile. The pile may also contain a few additional items: random gems, a ring or amulet, (if in an object-materials-implementing variant) a gold version of an item that is eligible to be gold. Atop the center of the pile is a dragon, or possibly a few adult dragons all of the same species, either asleep or flagged as waiting, with possibly a few dragon eggs of the same species and/or a couple baby dragons.
Dragons that generate at level creation time also spawn a hoard of gold beneath them, similar to how concealing monsters generate items to hide beneath. Possibly, their AI recognizes the horde as theirs and they are reluctant to stray off of it or far from it as long as there is gold there.
Rather than placing random amounts of gold on each tile in a special room that generates gold on each tile (zoo, leprechaun hall, and any other that might get added), bias it so that there is more gold in the corners and along the walls, on the basis that things tend to accumulate in the corners of rooms. Should work on irregularly shaped rooms as well as rectangular ones.
One possible algorithm is that corners get 3 “helpings” of gold placed on them, walls 2, and every other space 1.
Another take is to instead put more gold into the center of the room and less further out, possibly guaranteeing some dragons on top of the biggest piles.
Give a special message when you fail to tame a dragon as a knight (for whom it’s impossible to tame dragons under any circumstances).
Kicking a dragon while you are riding it as a steed makes it use its breath weapon (if it is currently able to, with its cooldown over). This is still subject to possible tameness penalties and other side effects of kicking a steed. It’s not defined whether the player should control the direction it breathes in or whether it will select a target itself.
Adult female dragons drop eggs (more so than the usual oviparous drop odds).
Dragons’ alignments are adjusted so that the values actually matter (at the least, yellow should be very lawful, gray should be pure neutral, and black should be very chaotic), and are not specified as M2_HOSTILE anymore so that they can rarely be generated peaceful. Perhaps more interestingly, their difficulties should be varied.
Wyverns and/or wyrms that share the D glyph but don’t have breath attacks. Probably brown colored, since no dragon uses that.
Excalibur starts out much weaker than it currently does, but you can perform further feats to enhance its power and give it more abilities as the game progresses. Such feats include: slaying a dragon, returning to King Arthur having finished the Knight quest, getting crowned as a lawful, re-dipping it into a fountain at a high experience level.
Tame dragons never drop scales.
Psuedodragons that are tiny D-class monsters. They may be the starting pet of Wizards, but don’t grow up. Instead, they have some kind of telepathic/psychic/magic-enhancing passive ability that scales with their level.
Dragons have a smaller chance of leaving scales if they are killed with a sharp weapon.
Carrying gold items openly causes leprechauns, dragons, and Croesus to be automatically aggravated.
A level sound for when there is a dragon somewhere on the level.
Dragons can cast spells.
Dragons, and probably all MZ_HUGE monsters, can’t enter corridor tiles or go through open doors because they’re too big. (This would probably mean that corrmaze levels in Gehennom would need to be removed or not generate huge monsters.)
Dragon with slowing breath. The effect stacks with previous effects of slowing breath.
Wind dragons, a cyan D whose breath is a wind beam: it doesn’t damage you, but blows you backward, and can’t be reflected. Their scales grant flight, which now confers resistance against knockback and Newton’s Third Law.
Buff late-game undead, because undead’s significance in Gehennom tends to be pointless since they aren’t scary by the time the adventurer gets there.
Add rumors to FIQHack that warn about dragons, which can be fairly dangerous.
