Source: The Book of Many Things

Wondrous Item, rare (requires attunement)

This marble-size crystal sphere glows with extraplanar energy.

As part of attuning to this item, you press the crystal sphere to the hilt of a nonmagical melee weapon of your choice, magically attaching the sphere to the weapon. The weapon becomes a magic weapon with a +1 bonus to attack and damage rolls. While wielding this weapon, you gain the following benefits:

Dimensional Anchor. You have advantage on saving throws against spells or effects that would send you to an extradimensional space, a demiplane, or another plane of existence against your will.

Isolating Smite. When you hit a creature with this weapon, you can force the creature to make a DC 16 Charisma saving throw. On a failed save, the creature is banished to a harmless demiplane until the end of its next turn. When the banished creature returns, it reappears in the space it left or the nearest unoccupied space if that space is occupied. Once this property is used, it can’t be used again until the next dawn.

When you end your attunement to the sphere, the sphere harmlessly detaches from the weapon, and the weapon reverts to a nonmagical piece of equipment.