Fargo's Mod/Rune Orb

The Rune Orb is a craftable item used to summon a Rune Wizard. It also can be bought from after one has already been defeated.

The Rune Orb will only work at night or if the player is underground (at or below the cavern layer). If used during the daytime or above the cavern layer, the Rune Wizard will not spawn and the item will not be consumed.