Source: Keys from the Golden Vault

Wondrous Item, Rare (Requires Attunement)

This 1-foot-long shard of obsidian has veins of silver and gold beneath its cold surface.

Empowered Magic. While holding the shard, you can use it as a spellcasting focus, and it gives you a +1 bonus to your spell attack rolls.

Enhanced Strength. Your Strength score increases by 4 while the shard is on your person. The shard can't raise your Strength score above 22.

Curse. Attuning to this item extends its curse to you. You remain cursed until you are targeted by a Remove Curse spell or similar magic, or until the shard is reattached to Xeluan's petrified heart.

The shard's curse causes misfortune to befall you. When you roll a 1 on an attack roll, an ability check, or a saving throw, roll on the Shard Misfortunes table to determine the misfortune. For as long as this misfortune lasts, no other shard misfortunes befall you.

Shard Misfortunes
d6 Misfortune
1 You accidentally cut yourself with the shard and are poisoned until the next dawn.
2 You experience a vision of an ancient calamity—a beautiful city threatened by crumbling mountains and erupting volcanoes—and are stunned until the end of your next turn.
3 For a few seconds, the ground shakes under you. You and each creature within 10 feet of you must succeed on a DC 16 Dexterity saving throw or be knocked prone.
4 The shard releases three glowing darts of magical force that target one random creature within 30 feet of you. If no such target exists, you become the target. Each dart hits automatically and deals 3 (1d4 + 1) force damage to the target.
5 Until the next dawn, Beasts with an Intelligence score of 3 or lower are hostile to you.
6 Nothing seems to go your way. Until the next dawn, you have disadvantage on ability checks.