Wondrous item, very rare or legendary (requires attunement)
The typical crystal ball, a very rare item, is about 6 inches in diameter. While touching it, you can cast the scrying spell (save DC 17) with it.
The following crystal ball variants are legendary items and have additional properties.
Crystal Ball of Mind Reading. You can use an action to cast the detect thoughts spell (save DC 17) while you are scrying with the crystal ball, targeting creatures you can see within 30 feet of the spell's sensor. You don't need to concentrate on this detect thoughts to maintain it during its duration, but it ends if scrying ends.
Crystal Ball of Telepathy. While scrying with the crystal ball, you can communicate telepathically with creatures you can see within 30 feet of the spell's sensor. You can also use an action to cast the suggestion spell (save DC 17) through the sensor on one of those creatures. You don't need to concentrate on this suggestion to maintain it during its duration, but it ends if scrying ends. Once used, the suggestion power of the crystal ball can't be used again until the next dawn.
Crystal Ball of True Seeing. While scrying with the crystal ball, you have truesight with a radius of 120 feet centered on the spell's sensor.