You can use a crystal ball to search for an artifact. It will not tell you where it is, but it will show you a “cloudy” image of the artifact if it already exists, and an “empty” image if it does not yet exist. Maybe also tell the player explicitly “It means this artifact is/is not anywhere in the dungeon right now.”

Premonition system: under various conditions (crystal balls, clairvoyance, dreaming while you sleep, the Oracle) you can receive a premonition of something that will appear later in your game (this could be almost anything: a monster, object, dungeon feature, special room, etc) which then has a very high chance of generating subsequently.

Crystal balls can accept words instead of symbols, such as “dragon” or “trap”.