Mimir

A mimir, also known as a Well of Knowledge or a Speaking Skull, was a variety of minor magical item unique to the Outlands that acted as a sort of encyclopedia.

Etymology
These magical objects were named by wizards after Mimir, an incredibly wise power of the Norse pantheon. Their alternative name, "Well of Knowledge," was likely inspired by the Well of Mimir, which some also referred to by the same name.

Description
Mimirs came in a variety of forms, including cubes, disks, leaves, stars, sunflowers (a popular choice among druids), human skulls, animal skulls, butterflies, rib-bones, leering imps, and many more. Regardless of their shape, a mimir was always made of a mysterious, silvery metal and had tight line patterns etched into it. This metal shone and would reflect light in rainbow hues. As no other object in the planes had ever been seen made of the same material, many assumed it was formed in the same process that created mimirs.

Powers
A mimir allowed one to record information for later playback. The amount of auditory information they could store was unlimited. When a user pointed at and asked a mimir a question, it would respond a few seconds later in an instructive, conversational tone with any information it had been instilled with by its creator on the given subject. If a user asked a mimir where they stood in the Outlands, it would respond by stating what ring (layer) outward from the Spire the user was standing in, rather than giving any exact distance or location.

Much like an ioun stone, these objects floated around and followed those who owned them. And unless allowed to float freely in air or water, a mimir would not respond to questions. They also would not function outside of the Outer Planes. If a user asked a mimir a question while on the Astral plane, the Ethereal plane, one of the Inner Planes, or a Prime Material plane it would respond with a babble of gibberish.

Being a magical object, mimirs could be temporarily disabled with dispel magic. The Silence, 15' radius spell and dead-magic zones would render them inoperable, but return to functioning once removed from. And if a feeblemind spell was cast on it, a mimir would be sent into a gibbering fit.

Availability
Mimirs were commonly sold in the Outlands, both in the city of Sigil and in the gate-towns. Across the Outer Planes, they were most commonly found in use in the Lower planes.

Price
On average a mimir cost two thousand gold pieces, though some considered a smarter option to be simply trading another magic item for one.

History
At some point, a group of adventurers from the Prime Material world of Toril came to the city of Sigil, having purchased a map from a sage in Shadowdale. When the group's fighter unfolded the map they began scanning it in search of the gate-town Glorium, only to quickly be corrected by his rogue ally that town headed to Gladsheim and they were looking for the gate-town to Bytopia. Watching the adventurers argue among themselves, a peddler emerged from the shadows with a variety of shaped mimirs floating about him. He offered a skull-shaped one to the group's fighter, who proceeded to ask it their query and was told what they sought was the gate-town Tradegate. Impressed, the adventurers paid the peddler for the mimir and went off on their journey.

Notable Users

 * Fiends often utilized mimirs in their endless Blood War to store battle plans, maps of enemy fortifications, espionage reports, and recordings of torture sessions.
 * Qaida, an aasimar and member of the Dustmen, owned a skull-shaped mimir.

Rumors & Legends
Where exactly mimirs came from or were made was a mystery. Some claim they came from chaotic good planes, while others believed they were spawned in the pits of Baator.