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. A more elegant term is beatitude (blessedness).
Noncursed (or !C) is a shorthand way of saying not cursed, i.e. blessed or uncursed. For many items, the blessed and uncursed usage are very similar, but very different from the cursed usage. For example, uncursed potions of gain level increase your experience level, blessed potions increase your level and get you well on the way to the next level too, but cursed potions of gain level will move you up through the ceiling, moving you up one dungeon level.
Generally speaking, blessing an item is never a Bad Idea. All blessed items are one step farther from being cursed, and they confer an 1d4 damage bonus when wielded as a weapon 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 has its 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 will never be rotten, and will 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 missiles (arrows, darts, throwing stars, etc...) have a significantly lower chance of disappearing when used.
- A blessed item generator generates blessed items.
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 equipped is reluctant to be taken off if it's cursed. This includes amulets, weapons, armors, 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 is used.
- 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 if it is cursed.
- The invocation ritual won't work if any of the three items (bell, candelabrum, and book) are cursed.
However, there are items which have special use as cursed, which is useful if you know they are cursed:
- 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.
- Cursed potion of gain level raises you to the previous dungeon level, which is useful when ascending with the Amulet of Yendor.
- Cursed scroll of teleportation teleports you between levels, which is especially useful if you have teleport control. Non-cursed scrolls have a similar effect if you are confused, but this can interfere with teleport control.
- Cursed scroll of gold detection shows traps as gold. However, non-cursed one shows traps as traps if you are confused.
- Cursed scroll of destroy armor can be used to fooproof a piece of armor if read while confused.
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, even if you have fully identified the item. Also, 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.
A scroll of identify will also show you the B/U/C status of an item.
Take note that after dropping it on a altar, a Scroll of scare monster can turn to dust after it is picked up.
Changing the B/U/C status of an item
There are quite a few ways to change the B/U/C status from items:
- Dipping an object into a potion of holy water will change the B/U/C 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.
- Dipping an object into a potion of unholy water will do the exact opposite, changing the B/U/C status from blessed to uncursed, and then to cursed.
- 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.
- If confused, a read scroll of remove curse will randomly curse 25% and bless 25% of all uncursed items to which the scroll would have applied if not confused (none if cursed, as named above if uncursed, all uncursed inventory if blessed).
- 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. Cursed scrolls of enchant weapon and armor will curse the item they target.
- 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).
- 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 reduces the amount of items that are cursed (but it will not nullify the attack), while Magicbane will "catch the curse" 95% of the time and totally nullify the attack.
- 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).
- When stepping on a magic trap, there is a 4.8% chance for an uncursing effect, equivalent to an uncursed scroll of remove curse.
- A blessed eucalyptus leaf may be applied and used as a magic whistle; this act has a 1/50 chance of removing the 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 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.
- Zapping a wand of cancellation at 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.
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.