Dragon Information

as appears in dragon.inf

Every breath weapon does 1/3 of the monster's current hit points, except lightning, which does 1/4.

Acid damage is then halved if you have any armor to corrode, or divided by 4 if you have resist acid and some armor.

Cold or fire damage is divided by 3 if you have permanent resistance (from a ring, armor, or weapon) or temporary resistance (from a potion or priest spell), and by 9 if you have both.

Lightning damage is divided by 3 if you have resistance.

Gas damage always has full effect.

Ancient Multi-Hued Dragon: (40/276)
2080 total hit points
lightning: 520/173
acid: 693/347/173
fire/cold: 693/231/77
gas: 693

Even a 40th level half-troll warrior with 18/100 constitution, heroism, and superheroism would probably not have 693 hit points. Thus you must never fight AMHD's if you are giving them any opportunity to breathe on you. I don't like to go down to level 40 unless I have 231 hit points and resistance, so that I can survive 4 out of 5 breaths from off-screen AMHD's.

Ancient Green Dragon: (39/269)
720 total hit points
gas: 240

Ancient White Dragon: (38/263)
704 total hit points
cold: 235/78/26

Ancient Blue Dragon: (39/268)
696 total hit points
lightning: 174/58

Ancient Black Dragon: (39/270)
720 total hit points
acid: 240/120/60

Ancient Red Dragon: (40/273)
840 total hit points
fire: 280/93/31

3000 total hit points
fire: 1000/333/111

Thus a mage with less than 333 hp can be killed by one breath from the Balrog, before he gets a chance to drink invulnerability potions. For a mage to get 333 hp, he must be human, and he must use the grape jelly trick.

Mature Multi-Hued Dragon: (38/262)
640 total hit points
lightning: 160/53
acid: 213/107/53
fire/cold: 213/71/24
gas: 213

Mature Green Dragon: (36/256)
384 total hit points
gas: 128

Mature White Dragon: (35/250)
384 total hit points
cold: 128/43/14

Mature Blue Dragon: (36/255)
384 total hit points
lightning: 96/32

Mature Black Dragon: (37/261)
464 total hit points
acid: 155/77/39

Mature Red Dragon: (37/260)
480 total hit points
fire: 160/53/18

Young Multi-Hued Dragon: (36/254)
320 total hit points
lightning: 80/27
acid: 107/53/27
fire/cold: 107/36/12
gas: 107