Burrower. The Thunder Egg can burrow itself into muddy soil and does so to keep itself safe from predators. It is most often found less than a foot underground.

Lightning Snare. If stepped upon while underground, the Thunder Egg releases a surge of electric energy. Each creature in a 5 foot radius must make a DC 12 Dexterity saving throw, taking 16 (4d6) lightning damage on a failed save, half as much on a successful one. Any creature that fails the save is also unable to take reactions or move until the beginning of its next turn.

Discharge. When the Thunder Egg is plucked from the ground by it's lightning rod, it releases a devastating shock to the creature that removed it. Any creature in physical contact with the Thunder Egg must succeed on a DC 15 Constitution saving throw, taking 24 (6d6) lightning damage on a failure, half as much on a successful one. Any creature that fails the save is also unable to take reactions or move until the beginning of its next turn. The Thunder Egg can only use this feature once per day.