BUC is an acronym meaning blessed/uncursed/cursed. It is usually used in phrases such as "BUC identified", meaning an item whose "BUC status" is known. Another term is beatitude (which technically means only "the state of being blessed", but in the context of NetHack generally means an object's relative blessedness, i.e. its BUC status).
Non-cursed is generally used to mean "either blessed or uncursed". This shorthand is useful because many items behave similarly whether blessed or uncursed, but very differently if cursed.
Generally speaking, blessing an item is never a Bad Idea. All blessed items are one step further from being cursed, and they confer an 1d4 damage bonus when wielded as weapons against the undead and demons (though this is mostly only useful for weapons). Also, some items confer additional bonuses when blessed:
- Most blessed scrolls and potions work better if they are beneficial, or have their harm reduced/nullified if they are harmful.
- Blessed spellbooks can always be read successfully, regardless of the spell's level, your level, or your intelligence score.
- Blessed tins require only one turn to open no matter what opening tool you use (or even if you use no tool at all).
- Some tools work better when they're blessed. Notable examples include bag of holding, unicorn horn, and touchstone. Blessed tools with charges will also resist the effect of a cursed scroll of charging.
- Wands cannot be harmed by cursed scrolls of charging if they are blessed.
- Blessed weapons do 1d4 extra damage to undead and major demons.
- Blessed missiles (arrows, darts, throwing stars, etc...) have a significantly lower chance of disappearing when used.
- Blessed items are resistant to erosion, with a chance depending on your Luck.
- A blessed item generator generates blessed items:
The one item which players often do not want to bless is a magic marker. Keeping it uncursed allows the player to write on cursed scrolls of blank paper to produce cursed scrolls, which a blessed marker cannot do.
A cursed item, on the other hand, is usually bad. Cursed items are more difficult to bless, and almost all of them will at least impede the item's performance, if not incurring an ill-intended effect.
- Anything that can be worn or wielded is reluctant to be taken off or put aside if it's cursed. This includes amulets, weapons, weapon-tools, armor, tin openers, iron chains, heavy iron balls, and rings.
- Potions and scrolls generally work worse if they are cursed: if they are harmful, the harm is generally amplified, and if they are beneficial, either the benefit is reduced/nullified or a totally different, usually harmful effect occurs.
- Wands have a chance of exploding when you zap them while they are cursed.
- You can never read a cursed spellbook successfully.
- Tools generally do not work as well when they are cursed.
- Pets will not pick up cursed items.
- Comestibles (but not corpses) are always rotten when they are cursed.
- A loadstone cannot be dropped or thrown while cursed.
- The invocation ritual won't work if any of the three items (bell, candelabrum and book) is cursed.
However, there are items which have special uses when cursed, if you know they are cursed:
- A cursed potion of gain level transports you one dungeon level upwards, which has several uses.
- A cursed potion of invisibility will wake all sleeping/meditating monsters on the level. Covetous monsters such as the quest nemesis, named demons, and the Wizard of Yendor will quickly warp to you after being awakened, allowing you to fight them without having to make your way to their location.
- A cursed scroll of genocide creates 4-6 specified monsters. This has many potential uses; to name a few: experience levels, maximum hit points, intrinsics, intelligence or strength gain, Luck, unihorn, dragon scale mail, or powerful pets. See Genocide#Reverse_genocide for details.
- A cursed scroll of teleportation will levelport you instead of regular teleportation, which is especially useful if you have teleport control.
- A cursed scroll of gold detection shows traps as gold. However, a non-cursed one shows traps as traps if you are confused.
- A cursed scroll of destroy armor can be used to fooproof a piece of armor if read while confused.
- A cursed scroll of confuse monster confuses you. This is useful if you don't have other sources of confusion.
- Pets are reluctant to enter a square with a cursed item (unless there is food in that square too). Because of that, cursed items can be used to restrict their movements, most notably in Sokoban to prevent them from getting stuck behind a boulder.
The NetHack encyclopedia has this to say about cursed items:
Curses are longstanding ill-wishings which, in Fantasyland,
often manifest as semisentient. They have to be broken or
dispelled. The method varies according to the type and
origin of the Curse:
4. Curses on Rings and Swords. You have problems. Rings
have to be returned whence they came, preferably at over a
thousand degrees Fahrenheit, and the Curse means you won't
want to do this. Swords usually resist all attempts to
raise their Curses. Your best source is to hide the Sword
or give it to someone you dislike.
An altar can be used to detect the beatitude of an item by means of the coloured flashes when the item is dropped on it, an amber flash indicates that the item is blessed, whereas a black flash means the item is cursed, if there is no flash the item is uncursed. Identifying an item this way is impossible when blind, and when hallucinating it is impossible to tell blessed and cursed items apart since the flash will appear different; however, the lack of a flash can still tell you that the item is uncursed.
For some items, such as gold pieces or scrolls of mail, the beatitude has no meaning and is always omitted. For some other items, such as weapons or rings with charges, it is not shown if the object is uncursed, if you have fully identified the item. Priests never see the uncursed-status, and can automatically tell the beatitude of any item they see, even if it has yet to be identified. If you want the game to override this behavior and show "uncursed" on every item you have identified as such, set the implicit_uncursed option to FALSE.
A scroll of identify will also show you the BUC status of an item.
A scroll of scare monster can turn to dust when you pick it up.
Changing the BUC status of an item
There are quite a few ways to change the BUC status of items:
Curse removal or blessing
- Dipping an object into a potion of holy water will change the BUC status from cursed to uncursed, and from uncursed to blessed, using one potion of holy water each time you dip it. Dipping a blessed item into holy water will not consume the potion and not wet the object.
- An uncursed scroll of remove curse will remove the cursed status from the wielded object (whether it is a weapon or not), all worn items (armor, rings, amulet, blindfold, towel, and lenses), any leashes currently in use, and any carried loadstones. A blessed scroll of remove curse will remove the cursed status from every object in your inventory. A cursed scroll of remove curse "disintegrates" and removes no curses, though it will still end any punishment.
- A non-cursed scroll of enchant armor or scroll of enchant weapon will uncurse the armor/weapon it targets. A blessed scroll of enchant armor will bless uncursed armor.
- Your deity may bless and repair your weapon or uncurse your inventory when you pray on an altar, depending on your Luck (see prayer for details).
- When stepping on a magic trap, there is a 4.8% chance of an uncursing effect, equivalent to an uncursed scroll of remove curse.
- #dipping items in fountains can curse and uncurse items (4/30 chance of uncursing, 1/30 chance of cursing). A fountain will never bless an item.
- When dipping a unicorn horn or amethyst into a potion which then transforms, the result is uncursed, except for juice made with a cursed horn or an amethyst, which is cursed.
Blessing removal or cursing
- Dipping an object into a potion of unholy water will change the item from blessed to uncursed, and then from uncursed to cursed.
- If you read a scroll of remove curse while confused, each affected uncursed object will have a 25% chance of becoming cursed and 25% chance of becoming blessed. The same objects are affected as when not confused, such as wielded objects, worn items, leashes in use, and carried loadstones.
- Cursed scrolls of enchant weapon and armor will curse the item they target.
- High-level spellcasting monsters (notably liches and the Wizard of Yendor) can randomly curse items in your inventory during combat. The message received is "You feel a malignant aura surround you." Magic resistance and half spell damage reduce the amount of items that are cursed (but will not nullify the attack), while Magicbane will "catch the curse" and nullify the attack 95% of the time when wielded.
- Quaffing from fountains can have a cursing effect on every item in your inventory (see fountain for details).
- #dipping items in fountains can curse and uncurse items (4/30 chance of uncursing, 1/30 chance of cursing). It is never blessed.
- A loadstone will curse itself automatically, making it impossible to drop should you pick it up again, and picking up a blessed scroll of scare monster will remove its blessing.
- The dunce cap and the helm of opposite alignment can be generated uncursed, but autocurse when worn, preventing you from removing them by normal means.
- A blessed eucalyptus leaf may be applied and used as a magic whistle; this act has a 1/50 chance of removing the blessing.
Removal of either curse or blessing
- Cancelling an item will remove any blessing or curse, but may also have other (probably detrimental) effects such as removing enchantment or emptying a wand of charges.
- Alchemy results are always uncursed.
In-game, the phrase "Items of unknown B/C/U status" appears in the drop menu, but the "BUC" ordering is more common in discussions.