Sword of Prophecy (Patreon)

This legendary magic weapon is not only a tool of the battlefield, it grants you the power to (possibly) foretell the future.

The sword does let you use a 9th-level spell, but at the cost of it losing all of its magic for an entire month.

And yes, it does have what looks like a small version of Magic 8-Ball for a pommel. Instead of a floating polyhedron, this item uses actual magic.