NetHack/YMMV


 * Breather Boss: Croesus is a pretty tough foe in melee and fast to boot, but is much easier compared to the quest nemeses and other bosses, and can easily be dispatched in various ways.
 * Broken Base: Two of the major arguments in fandom have been:
 * Should the game be played using the graphical tile-sets or the original ASCII format?
 * Is it a legitimate tactic to exploit programming quirks which allow such things as "pudding farming" (see below)?
 * The changes to the protective ward "Elbereth" in 3.6.0 were also a significant Base Breaker, to the point that 3.6.1 walked a few of them back.
 * Demonic Spiders: There's at least two or three at any point:
 * On early levels, you have to deal with floating eyes which paralyze you, gas spores which do obscene damage by exploding when they die, and killer bees that can poison and instakill you. Floating eyes can be avoided, killer bees can be Elberethed, but may The Lady help you when your overleveled pet decides to start attacking that gas spore that's adjacent to you...
 * On early-middling levels, you have to deal with soldier ants -- the most common enemy-based cause of death in the game (accounting for 1.75% of all deaths on nethack.alt.org. Go team ant!)
 * On the middling levels, you have the infamous cockatrices and many enemies who can swallow you and kill you, including lurkers and purple worms (which can also be encountered on the earlier levels).
 * Then you must contend with Demon Lords and Princes, and should you actually survive them and get the Amulet of Yendor, you must face the Wizard of Yendor,
 * Excuse Plot: There is an amulet in this dungeon. You need to find it, then return it to your god. Go. The details and quest branch vary with each class, but ultimately the basic plot progression is the same.
 * Fridge Horror: There are lots of "used armor" shops scattered throughout the dungeons. Sometimes these shops contain cursed armor, which can't be removed, except by uncursing it or if the original owner dies wearing it. The horror comes when you realize where the shopkeeper gets his inventory.
 * And if you die in a shop, the game flat-out tells you that the shopkeeper takes all your possessions. If you somehow directly steal from the shop (e.g. teleporting out with unpaid items, digging out...), the shop owner will chase you. When you die, guess who comes for the loot?
 * Game Breaker: A very controversial thing to do in Nethack pre-3.6.0 is "Pudding Farming", causing an enemy that splits into two whenever you attack it to split multiple times to abuse the game's prayer and sacrifice systems. A similar thing is to repeatedly kill a boss that is on the last level of the game. This boss reincarnates an infinite number of times, but gives a full score each time, meaning with the proper setup, hitting the max score is trivial (but that's OK, since in Nethack, it's generally considered a sign of skill to ascend with a lower score rather than a higher one).
 * The joke goes that the DevTeam implemented an immediate and savage punishment for pudding farmers. Also, nearly anything you'd accomplish with pudding farming won't help you as much on the astral plane.
 * Genius Bonus: Many things in Nethack, including some of its Shout-Outs, are very subtle. For example, there is an enemy named the "quantum mechanic" which sometimes carries a box. Inside the box is a cat named Schrodinger's cat, which has a 50/50 chance of being either alive or dead. If you examine the game's source code, you will learn that the state of the cat is not determined until you open the box. Some fantasy items benefit you if you know the myths without even having read a spoiler:
 * Since the game has strong Unix origins, there's also plenty of jokes only a Unix/Linux geek would understand.
 * Goddamned Bats: Nymphs, Floating Eyes, and Leprechauns, to name a few.
 * Scrappy Level: Gehennom is actually 20 to 24 consecutive Scrappy Levels. One of the many additions SLASH'EM makes is breaking up the monotony of Gehennom with more "special" levels, while Sporkhack completely revamps Gehennom by (a) giving the local Mooks some ability to actually threaten the player (b) getting rid of the mazes in favour of caves (with lava behind the cave walls).
 * "Stop Having Fun!" Guys: Don't get caught using any movement key configuration other than HJKLYUBN.
 * Or maybe numpad.
 * That One Boss: Master Kaen (the Monk quest nemesis) and Demogorgon both qualify, as does the Wizard of Yendor, due to his propensity for coming back with more hit points and a higher caster level than before.