Planescape - Adventures in the Multiverse
Wondrous item, Rare (Requires Attunement)
This skull shaped device is filled with knowledge.
The device weighs 5 pounds and is covered with subtle etchings of planar sigils.
As a bonus action, you can toss the device into the air, whereupon it floats at a distance of 1d3 feet from you and you can access its properties. While the mimir is floating, a creature other than you can use an action to grasp or net the device, either by making a successful unarmed strike against AC 22 or a successful DC 22 Dexterity (Acrobatics) check. You can use a bonus action to seize and stow the device.
The device has AC 22, 25 hit points, immunity to poison and psychic damage, and resistance to all other damage. It is considered to be an object that is worn while it is floating near you.