How well a “joke” goes always varies, but this had clearly gone too far. The water mephits almost drowned one of the confused crew members before the sailors realized what was happening. The crew pushed back the deadly pranksters and saved their friend from the depths of the river.
Soon after, the laughing elementals came back like scolded children, miserable and ashamed.
“Uhm… Look, we’re very sorry you almost uh… drowned. The Drowned Rat won’t like this, not at all. He never really like our jokes, but he’ll be VERY crossed if he hears about this. You’re not going to tell on us in your prayers, right?”
“I just might.” said the rescued sailor, drenched and still covered in mud.
Throwing themselves on the deck, whining and crying, the mephits begged.
“Please mister, we weren’t gonna drown anyone, look we were gonna give you some Dulaman and you would have been fine! It would have been so fun! You can keep all of it, we know a good spot to find it. It’s all fine now right mister, you’ll tell the Drowned Rat that, you’ll say we’ve apologized?”
A few sessions ago my players had an encounter with water mephits who like to have fun with the boats trying to navigate on their river. No one was really harmed, but the “joke” made the adventurers understandably angry. As an apology, the mephits gifted them a few doses of this rare item.
The name “Dulaman”, or Dúlamán, is the name of a type of edible seaweed that’s gathered in Ireland and a reference to an Irish folk song I love. I’ve also written a sort of mythical character of the same name, a legendary sailor of the region who sailed along all its rivers.
I’ve used the Water Breathing Potion as reference for the level and price, and I feel this is similar in balance. You can extend and empower the effect, but I think the negative effects counterbalance it nicely. Essentially, this can be used if you want to stay in the water for a while, but you have to commit to it.