The player can polymorph briefly into a random monster, gaining all its abilities.
There are magical items that let you control your transformation, change gender or remain in a form indefinitely.
Female snakes, birds and dragons can lay eggs.
Conclusion: whilst playing as a female character, polymorph into a cockatrice, lay dozens of eggs, revert to human, and throw the eggs at enemies to petrify them instantly! ...And the DevTeam has even thought of that, as causing your own eggs to break carries a significant guilt penalty to your Luck Stat.
A cockatrice corpse can be wielded as a weapon (if you have gloves, of course), which will handily petrify enemies... until it starts to rot.
...But, as with all corpses (and other food items), you can dip it in holy water to bless it, which keeps it fresh for much longer.
Also, if one falls down a staircase while wielding a cockatrice corpse, bad things tend to happen...
Perhaps the best example of this involving cockatrices is this. When you are blind and walk over an item, the game states "you try to feel what is lying on the floor. It is a [item]." This is literal; if you walk over a cockatrice corpse while blind and bare-handed, "you turn to stone..."
Touching a cockatrice corpse without gloves will also instantly petrify the player if the cockatrice corpse is in a container (chest, box, sack, bag of holding, oilskin). This has killed at least one player on the Astral Plane, who blinded themself to use Telepathy, took off their gloves for some reason, then searched in their Bag of Holding. Presumeably searching a container while not blind will not cause the player to touch the corpse.
Engraving Elbereth on a square and standing on it will stop monsters that respect Elbereth from attacking you in melee. Such monsters may also not step on a square with Elbereth engraved on it.
Therefore, such monsters with ranged attacks will switch to it while you stand on it, unless you engrave Elbereth while being adjacent to said monsters, causing them to flee.
Monsters already fleeing from Elbereth will not attack you, even they have ranged attacks.
Therefore... you can trap said fleeing monsters by surrounding them with Elbereth squares!
Beware, because blinded monsters can't see Elbereth, so they will NOT respect it.
Elbereth can be engraved permanently with Wand of Lightning or Wand of Fire. It will protect your stash from hostile monsters permanently. Such squares will revert to normal squares if you engrave with Wand of Polymorph on it. Also, keep in mind that using the wand of lightning will blind you if you don't have suitable protection.
Non-permanent Elbereth engravings degrade over time if you move on it, attack someone while on it, or if you just stand on it, as you cannot stay perfectly still.
If you are levitating on it, however, the engravings does not degrade whatever you do, and monsters will still respect it.
Elbereth is case sensitive. It will still work if you write in minor cases, but if you write it with proper capitalized E, you will exercise wisdom.
As a minor example, reading a cursed scroll of amnesia causes you to forget everything with the phrase "Thinking of Maud you forget everything else." or "Who was that Maud person anyway?" If your character is named Maud, the phrase is instead "As your mind turns inwards on itself, you forget everything else."
Try to dip a potion into itself and you get told "This is a potion bottle, not a Klein bottle!"
In a similar fashion, attempting to put a bag inside itself produces the response that "That would be an interesting topological exercise."
If you try to flash a camera underwater, you're told you can't do that because it would void the warranty.
Trying to apply a saddle to a succubus abuses your wisdom and produces the message "Shame on you!"
"Thou hast angered me." If you anger a god enough to earn divine retribution, you will be zapped with a lightning bolt. If that fails, you are zapped with a wide-angle disintegration beam. If that fails, the god says "I believe it not!" and gives up (except in the final level, where it gets even angrier). Although you can survive these with a ring of shock resistance and black dragon scale mail (which provides disintegration resistance), you can also survive by being engulfed by a monster: the beams will hit the engulfing monster before they hit you. If the monster has shock resistance, but not disintegration resistancenote No such monster exists in the vanilla game, but the code is in place anyway, just in case you try modding., it will survive the lightning bolt, but die to the disintegration beam, freeing you. And then you get experience points for pulling that off. But don't think you can keep a pacifist conduct this way.
Using a stethoscope towards the bottom of the screen (The 'j' direction) results in the fourth-wall noting line, "You hear a faint typing noise".
The player-character must be at the very bottom of the screen, just above the Status Line. Only a few levels permit the player to get to that location, even after digging. That's because level maps are bounded by walls that are "too hard to dig" if the meaningful area is smaller than 80x21.
Getting acid wet (by trying to #dip a potion of acid into a potion of water, for example) causes it to boil and harm the player. If this kills the player, their tombstone will list the cause of death as "elementary chemistry". This is notable in that most causes of death are reported in a matter-of-fact manner approaching Deadpan Snarker-levels ("killed by a grid bug while helpless", "killed by kicking a stethoscope", etc.), so one would be forgiven for not expecting a Take That directed at the player.
Additionally, throwing a cockatrice corpse up (<) will result in it hitting you on the head and, unless you're wearing a helmet, petrifying you instantly. Cause of death? "Elementary Physics"
Vaults full of gold are occasionally found sealed off from most of the dungeon. If you connive your way inside, a vault guard will appear to investigate. In most cases, he'll demand your name; most answers will lead to the guard demanding you leave all the money behind in the vault as the guard seals it back up. If you tell the guard that you're "Croesus" (alternate translations "Kroisos" and "Creosote" can be found acceptable as well), the guard will leave without incident. If you're a lawful-aligned character, you receive a small alignment penalty for lying, unless you actually named your character Croesus, in which case no penalty is incurred. If you try to pass yourself off as Croesus after you've gone to Fort Ludios and killed him, the guard gets angry and attacks. If you're unable to speak (e.g., an amulet of strangulation is choking you), the guard leaves. If you're mimicking an object (most likely having eaten a mimic's corpse, turning you into a pile of gold), the guard also leaves. If hallucinating when you eat a mimic corpse, you turn into an orange. The guard leaves puzzled, wondering "who left that orange in here". And if you're polymorphed into a small enough monster, you can hide under the gold and puzzle the guard again. If you're changing body armor (which can take four turns, or longer), the guard leaves commenting that he'll return when you're not busy.
Another one: eating a flint stone would result in the message "Yabba-dabba delicious!". Currently no monster can eat rocks, so this isn't actually seen. Flintstones brand of children's vitamin tablets.
If you eat too much, you choke and die. Makes sense. Unless you're wearing an Amulet of Magical Breathing. Also makes sense!
Speaking of amulets of magical breathing, the polar opposite is the amulet of strangulation, which kills you in five turns unless you can get it removed. But what about the "unbreathing" property (from equipping or eating an amulet of magical breathing, or polymorphed into a creature with the property)? The amulet strangles you anyway because the constricting action cuts off the blood supply to your brain, with different text to match!
They even do this in the download! "Step 0: Promise to do step 2 before telling us the game won't run. Thank you."
Eucalyptus leaves can be eaten to cure food poisoning, as intended. Or, you can Apply the leaf instead of Eating it to use it as a noisy grass whistle. This also has a chance of removing the blessing from a blessed leaf, because seriously, you just put your mouth all over it.
The infamous Floating Eyes cannot counterattack while blind, but the player has a chance to lose luck while finishing the Eye off because beating up blind people isn't cool.
With some "luck", it is possible to kill yourself on turn 1 (e.g. as a knight, slip off your saddled pony trying to mount it or zap an attack wand at yourself). The resulting message: "Do not pass Go. Do not collect 200zorkmids."
Zapping a cream pie with a wand of striking gives the message "What a mess!" and destroys the cream pie. Applying a cream pie will blind you for a few turns, as your character just shoved their face into a cream pie.
The spell of "turn undead" causes undead creatures to flee, as per Dungeons & Dragons. What does a Nethack "wand of undead turning" do?
Why, makes undead run away of course... and also resurrects corpses.
And if you happen to be undead, it will stun you if you hit yourself.
The Mail Daemon delivers mail to the player. He spawns, delivers the mail and vanishes in one turn. However, you can wish for a statue of a mail daemon, cast Stone To Flesh and the Mail Daemon will spawn, say "I'm late!" and vanish.
As a side note, if you're good enough, you might be able to kill this Mail Daemon before it vanishes. Doing this will genocide the mail daemon and prevent you from receiving any mail in the future.
Unlike normal scrolls, scrolls of mail can't be blanked or polymorphed (in order to prevent exploits by sending yourself dozens of mails and turning them into something useful).
The Quantum Mechanic monster is basically one big physics joke. Its attack will randomly teleport you, and eating a Quantum Mechanic corpse will give you the intrinsic speed ability (or remove intrinsic speed from you if you were already fast). Upon death, the Quantum Mechanic also has a small chance to drop a box. When you open the box, a cat named Schrödinger's Cat will be found inside. 50% of the time, the cat will be alive, and 50% of the time, the cat will be dead. What brings this into The Dev Team Thinks of Everything territory is that if you look at the game's source code, you discover that unlike every other box in the game, the state of the box's contents (whether the cat is alive or dead) is not determined until you open the box and look.
As a knight (who starts with a pet pony), play the game without a default horse name set and don't give it a name. If you go up on the first level with your horse, you're told that you've "been through the dungeon on a horse with no name". Dismounting an unnamed steed while hallucinating generates the message "It felt good to get out of the rain."
Removing a blindfold while blind for some other reason results in the message "You were wearing a blindfold. You still cannot see".
Certain classes of objects (wands, potions, and rings) have randomized appearances. For example, a "spiky wand" might always be a wand of death in one playthrough, and always a wand of cancellation in the next. However, there are certain ways that the appearance itself is meaningful, regardless of what the item actually turns out to be:
A smoky or milky potion might spawn a djinni or ghost, respectively, when quaffed.
Marble wands are affected by Stone To Flesh. Glass and crystal wands shatter when hit with a force bolt. Metal wands can rust. Copper wands can corrode. Silver wands can be wielded to do silver damage.
Rings set with hard gems can be used to engrave messages. And rings made of stone or gems can be turned into meat rings via the Stone to Flesh spell. Wearing a silver ring and attacking monsters bare-handed will cause silver damage, as long as you're not wearing gloves.
Here's a quick list of some of the more ingeniousnote And deliberate. So no bugs like "drowned in a drowning" or "turned to slime by a scroll of genocide." death messages, along with spoiler'd instructions on what causes them:
Dragged downstairs by an iron ball. You were punished, and walked in such a way that your iron ball went over a down staircase, and were killed by the resulting damage.
Squished under a boulder. You were in a pit, and a boulder was rolled or thrown on top of you.
Petrified by trying to help a cockatrice out of a pit. Pretty self-explanatory, but still demonstrates the trope.
Killed by dangerous winds. You were levitating over a Sokoban hole, and were killed by the fall damage.
Killed by wedging into a narrow crevice. You were carrying more than 600 weight of items, and you threw an item while levitating in such a way that Newton's 3rd Law forced you through a diagonal space between two walls.
Killed by an unsuccessful polymorph. You polymorphed into a form that would have had 0 or less max HP.
Killed by a residual undead turning effect. You polymorphed into an undead monster and prayed to a non-chaotic god, causing him/her to kill you.
For some scrolls and potions, if you use them when you don't yet know what they do and there's nothing available for their effects to act upon (like drinking a potion of monster detection when there aren't any monsters on the level) then you'll get the message "You have a strange feeling for a moment, but it passes". But if this happens while you're hallucinating, you get the message "You have a normal feeling for a moment, then it passes".
Get hit with a Finger of Death spell while polymorphed into an undead creature and the game informs you that "You seem no deader than before." Get shot with a Wand of Death and it notes that "The wand shoots an apparently harmless beam at you."
If, when trying to bribe a demon lord to leave you alone, you enter a negative number as the amount of gold pieces to give, the demon attacks you for trying to short-change it.
Armor (shirts, body armor, and cloaks) must be put on in the specific order of shirt first, then body armor, then cloak. They must also be taken off in the reverse order. If you're wearing, say, a cursed cloak, you can't unequip the armor under it, and you can't put any armor on over it.
Also, cursed equipment cannot normally be removed in anyway other than uncursing them. However, if you are wearing for example a cursed armor and you physically change form, such as drinking a potion that transforms you into a dragon ten times your original size, the cursed armor will break and fall off.
If you're blind, gaze attacks will have no effect on you.
If you are blind, hallucinating, confused or polymorphed into certain monsters, almost every single message in the game has a unique variant to account for your altered perception, such as describing the sounds instead of the visuals. Sometimes there are four or five different versions for if you have multiple effects at the same time.
Attempting to engrave with a Wand of Striking gives the message "The wand unsuccessfully fights your attempt to write!".