Jar of Lightningflies (Patreon)

Wondrous item, rare

This blue glass jar was made with sand that was struck by lightning, fusing it into a glass that was then remolded into the vessel. When found, there are 2d4 miniscule, fluttering sparks inside the jar, called lightningflies. While at least 1 lightningfly is within the jar, it sheds bright light in a 10-foot radius and dim light for an additional 10 feet.

You can use an action to unstopper the jar and allow any number of lightningflies to leave it; each one immediately vanishes with an electrical pop. For each lightningfly that leaves, a tremendous pillar of lightning crashes down on a different creature of your choice that you can see within 60 feet of you. A chosen creature must make a DC 15 Dexterity saving throw. On a failed save, the creature takes 4d10 lightning damage and emits a luminous glow until the end of your next turn, shedding dim light in a 10-foot radius for the duration. On a successful save, it takes half as much damage and doesn't emit the glow. Any attack roll made against a glowing creature is made with advantage.

The jar ceases to be magical while there aren't any lightningflies in it. However, if the jar is struck by naturally occurring lightning, there is a 10 percent chance that another 2d4 lightningflies reappear inside it, making it magical once more.

A fluttering spark, a sudden storm, and darkness once more.