Far Realm Shard

From Tasha's Cauldron of Everything, page 127.

Description
Wondrous item, rare (requires attunement by a sorcerer)

This writhing crystal is steeped in the warped essence of the Far Realm. As an action, you can attach the shard to a Tiny object (such as a weapon or a piece of jewelry) or detach it. It falls off if your attunement to it ends. You can use the shard as a spellcasting focus while you hold or wear it.

When you use a Metamagic option on a spell while you are holding or wearing a shard, you can cause a slimy tentacle to rip through the fabric of realm and strike one creature you can see within 30 feet of you. The creature must succeed on a Charisma saving throw against your spell save DC, or take 3d6 psychic damage and become frightened of you until the start of your next turn.