Wisp in a Bottle

The Wisp in a Bottle summons a wisp, a floating ghostly skull, to provide light. It serves the same purpose as the Shadow Orb or the Fairy Bell, but the Wisp not only keeps pace with the player, it actually moves ahead in the direction the player is moving. This can be used to see a short distance through walls. It cannot be used together with the Shadow Orb or the Fairy Bell, and summoning either will dismiss the other. The Wisp in a Bottle can rarely be dropped from Blue Armored Bones, Hell Armored Bones, and Rusty Armored Bones.

Trivia

 * The Wisp in a Bottle might be a reference to the series The Legend of Zelda, particularly Ocarina of Time when Link is adult, where you can capture ghosts with empty bottles and sell them or use them later.
 * Wisp may refer to Will-O'-the-Wisps, mythological creatures that lead travelers to their death in swamps.