Unique item

In NetHack, all artifacts are unique, but there are four objects which the game specifically refers to as unique items:

• The Candelabrum of Invocation
• The Bell of Opening
• The Book of the Dead
• The Amulet of Yendor

These items are defined with the tag OC_UNIQUE in objects.c, and the discoveries page also refers to these as unique items. While these are also commonly referred to as "invocation artifacts", they do not count as actual artifacts for purposes of artifact wishing, as the player is always guaranteed to encounter them.

Distinguishing from other "one-per-game" items

Artifacts are not unique items in the sense of this article; they are specially named variants of their base item with additional benefits. For example, the Eye of the Aethiopica is a named amulet of ESP that also provides faster energy regeneration among other extra powers.

While Stormbringer is the only runesword and the Tsurugi of Muramasa the only tsurugi that can normally be generated in a game, neither counts as a unique item; it is possible to find a non-artifact runesword or tsurugi in a bones file (if the artifact has already been created), or by wishing for one.

Variants

EvilHack

EvilHack adds several more "one-per-game" items:

• The Magic 8-Ball
• The Bag of the Hesperides
• Lifestealer
• Butcher
• The Wand of Orcus

While they do not share the same OC_UNIQUE tag as the invocation items and are considered actual artifacts, they also do not count towards the total number of artifacts in a game, as they are generated in ways that mean they are guaranteed to appear.