Azule's Seashell (5e Equipment)
From D&D Wiki
Wondrous item, rare
When you use your action to throw this tiny, blue-colored seashell (Is that a glowing eye inside it? Ew.), it will identify which creature within a 120-foot radius has the most remaining hit points, then immediately fly in a direct path towards that creature and explode with a fiery burst on impact, destroying itself in the process. The target takes 2d4 piercing damage. The target and all creatures within 10 feet of it must make a Dexterity saving throw (DC 15), taking 6d10 fire damage on a failure and half as much on a success. If the target fails the saving throw, it is also stunned until the end of its next turn.
If you throw this shell but have the most hit points out of all creatures in a 120-foot radius, there is a 25% chance the shell will target you and explode instead of seeking another creature.