Concussive Waves (Merfolk-only Feat)

General Feat

While you are fully submerged in water and your targets are fully or partially submerged in the same body of water, you can use a bonus action to beat your tail back and forth or up and down, releasing a concussive wave in a 15-foot cone. Creatures of your choice in that area must make a Constitution saving throw (DC = 8 + your proficiency bonus + your Strength modifier).

On a failed save, a creature takes thunder damage equal to 1d4 + your Strength modifier. Until the start of its next turn, it cannot take reactions and has disadvantage on the next attack roll it makes before the end of its next turn.

On a successful save, a creature takes half as much damage rounded down and suffers no additional effects.

You can use this feature a number of times equal to your proficiency bonus, and you regain all expended uses when you finish a long rest.