Acid Seaweed from the Feywilds

Acid Seaweed is a homebrew creation of mine, which attacked my unsuspecting players as they swam into the feywilds. If you think your players will enjoy being attacked by plantlife and want to use my creation in your campaign, click here to add it to your D&D Beyond profile. If you don’t use D&D Beyond, bookmark this page ready for your encounter instead, or you print off the stat sheet!

Backstory Around Acid Seaweed

Acid Seaweed is a carnivorous plant that eats whatever fleshy creature that swims into its path. Found in the feywilds, the blue foliage is dotted with pink spots which almost look like gems. These spots glisten in the water, enticing adventures down to the murky depths of the sea.

If water portals to the feywilds are left uncared for, the seaweed will start to spring to life in the overgrown waterways of caves, pond beds, and lake shallows. They are ready to digest anyone brave or stupid enough to walk into their path. 

Adventures must slash their way through the water grass if they want to visit the magical land of The Fey.

Ideas on How To Play The Acid Seaweed

I used this seaweed to cover a 100ft path which is only 5 ft wide. Looking at the “large” size of the seaweed, you may be wondering how I made the creature fit. Instead of assuming the large size meant the classic square shape, I opted for 4 5ft squares in a line instead.

Each 5ft path became a 34 hit point space so that the spaces matched the appropriate size. 

The only problem you may have now comes from opportunity attacks. I didn’t allow the plant to take opportunity attacks unless the players had walked past the 4th square. Large creatures are meant to take up a 4 square radius, so instead, having a 4 square line balanced out the encounter. 

When the players got to the 4th square, a surprise opportunity attack started, creating fear in my players and power in my plants!

Because the plant is attached to the water bed, it cannot move. You may want to create your own homebrew acid fish which lives in the seaweed. The creatures could work together to hunt prey and attack any adventures that try to escape!

How Did My Players React?

The 100ft tunnel held 5 Acid Seaweed beds, but unfortunately for me, the party was smart and took their time before entering into the water path.

First, the Circle of the Moon Druid cast Water Breathing, allowing the party of three to swim through the vast lake without worrying about drowning.

Next, the Swarmkeeper Ranger rolled a history check as plants were a favored enemy against her bees. With a high roll, she told the team that the plants were carnivorous and they should be cautious. 

Already preparing to protect his friends, the Path of the Totem Warrior Barbarian took the lead in the 5ft wide tunnel. He funneled all the attacks onto himself while the rest of the party fought behind him. The Bear Totem Warrior is resistant to all damage when they rage, except psychic, so the party’s Barbarian was an impossible shield that my plants couldn’t break through!

Honestly, the party couldn’t have done better!

I created a monster that used all of their best talents, and everyone felt useful and valued in the attack against vegetation. 

If I wanted to make the plants more of a challenge, I would give them a walking speed to leap onto their opponents after they have grappled them, or I could have made the tunnel wider. Overall, I was happy with the outcome!


Like what you see, have homebrew ideas of your own, or want to add some suggestions? Talk to us in the comment section! We would love to know how you would expect an encounter with a bed of Acid Seaweed will go with your party!


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