The Best Monsters For An Aquatic Setting In DnD

Updated Jul 19, 2026, 5:24 AM EDT Jerel Levy is an Evergreen Editor at TheGamer and has been working in gaming journalism since 2014. With a Bachelor's of Arts in English, his work first started at smaller websites before moving on to contribute at IGN and finally settling at TheGamer. He's been to Pax and Summer Game Fest for reporting, and has a specific focus on MMORPGs, JRPGs, mobile gaming, and Tabletop gaming, specifically Dungeons & Dragons and Disney Lorcana. Jerel delves deep into the best builds and options for these titles, providing excellent guidance for players of every skill level. Aquatic adventures, whether they be on a ship, underwater, or even in the elemental plane of water, can be one of the most memorable adventures in Dungeons & Dragons. Many modules are set around exploring uncharted waters, and they are one of the favorite biomes for players to experience. Setting up encounters for aquatic settings might require a lot of preparation and research. But knowing some of the most common and interesting inhabitants of these biomes can help you come up with various encounter ideas for your game. Updated on July 19, 2026, by Niall Walsh: We've added another monster to this list following the release of Ravenloft. The new campaign doesn't bring a ton of aquatic horrors to the game, but there are definitely some worth talking about. 28 Wretchglow, The Last Light The Scariest Underwater Encounter Wretchglow, the Last Light by Mark Witton Monster Challenge Rating Wretchglow, The Last Light 10 This deadly sea creature brings both a prehistoric and magical nature to your aquatic adventure. If you're looking for a true sea monster, Wretchglow is the perfect option. Reminiscent of the scariest deep-sea monsters your players can conjure up, they'll be shocked as they encounter the pulsing bioluminescent light that leads to the jaws of death. With legendary actions to direct the currents, preventing the party from making a quick escape, as well as attacking with its hooked claw and needle-toothed jaws, it's a Huge beast they'll never forget, if they live through the encounter. Even better, it can be hidden, so it's a great boss battle to sneak against the party as they traverse the deep depths. 27 Mosasaurus An Intimidating Presence Mosasaurus by Mark Witton Monster Challenge Rating Mosasaurus 11 The Mosasaurus is another large creature that any party would freeze if they encountered it underwater. With a Resistance to Cold, Lightning, and Thunder damage, spellcasters might have a hard time dealing with this Huge creature. Its Stormrider ability also gives it Immunity to Control Water and Tsunami effects, so don't think they'll be able to just maneuver it out of their way either. The Mosasaurus makes both a Piercing attack and an attack that deals Thunder damage, so it'll be sure to ignore someone's Resistance in the party. It also has Tough Hide and a decent AC, so good luck trying to deal with this dangerous creature. 26 Deinosuchus Resistant To Everything Deinosuchus by Mark Witton Monster Challenge Rating Deinosuchus 11 Gapple and restrain the party with a battle similar to fighting a gator, thanks ot the Deinosuchus. It's a hybrid creature, so you can use it in aquatic settings that are underwater and shallow or closer to land. It can hold its breath for an hour, and when underwater, it gets Advantage on Stealth checks. The most dangerous part of the Deinosuchus is its Hyper Resilience. It's Immune to Poison and resistant to all damage. With a hardy 18 AC and a decent health pool, it'll definitely be a DPS or strategy check for your aquatic campaign. 25 Seth The Shapeshifting Dragon Don't Be Fooled By His Origin Monster Challenge Rating Seth The Shapeshifting Dragon 10 This powerful dragon is separate from the others on this list as he's from the release of Misplaced Monsters: Volume One. In partnership with Extra Life for Children’s Miracle Network Hospitals to raise funds, several kids got to design their own monsters, which were eventually turned into full-stat monster options for any campaign. Seth the Shapeshifting Dragon is a very powerful dragon that is completely invisible while submerged in water, has a breath weapon that shoots frigid water, and has ridiculous bursts of speed to catch any creature trying to get away. Seth can change shape at will, has super speed that gives disadvantage to any creature trying to attack him while it's active, and his Riptide Breath shoots in a cone that'll deal heavy damage to anyone caught in it. He's a monster of a beast that'll present a true challenge. 24 Lorwyn Merrow The Sly And Cunning Cousins Monster Challenge Rating Merrow Haranguer 5 Merrow Doublespeaker 4 Unlike their vicious cousins, the Merrow of Lorywn, found in Lorwyn: First Light, are described as prideful and diplomatic. They're great at language and can take anyone on in a fight of words, making them great for a campaign where you need to make a connection between sea dwellers and land dwellers. They're also great for presenting a fun mix up to how aquatic creatures are shown and treated. The Shadowmoor and Doublespeaker Merrow are cunning and will easily trick an adventuring party out of everything they own if given the chance. You'll lose your treasure and your life as described in Lorwyn: First Light when messing with this variant. They are all great opportunities for aquatic campaigns that'll give players a chance to speak and interact with intelligent yet cunning beings. Frost Giant Of Evil Water Amphibious Giants You Should Fear Frost Giant of Evil Water by Olivier Bernard Monster Challenge Rating Frost Giant Of Evil Water 11 If you want a more pronounced water giant to add to your campaign and don't want to rely on the generic frost giant, the Frost Giant of Evil Water provides a few key specifications you'll find useful. Betraying the order, these gians are gifted the ability to breathe underwater, and they're outfitted with items such as harpoons that help them hook and drag creatures into the sea. They're generally evil and can make a great disruptor in an aquatic campaign, especially by placing one in the deep underwater or having one drag the party down to the depths. They're also not quite as strong as Frost Giants, so you can use them without fear of annihilating the party in one hit. 23 Merfolk Under The Sea Art by Andrea Piparo Monster Challenge Rating Merfolk Skirmisher 1/8 Merfolk Wavebender 6 Not every monster needs to be an enemy. If you want to have underwater civilizations, the basic Merfolk works perfectly to be the 'commoner' of your story, though a group of them can still be a challenge for low-level characters. They also have a CR six variant, which allows them to hit harder and have access to some spells that relate to water, such as Control Water, so they don't need to be just weak minions or commoners during the adventure. 22 Kuo-Toa With Weird Gods Art by Eric Belisle Monster Challenge Rating Kuo-Toa 1/4 Kuo-Toa Whip 1 Kuo-Toa Monitor 3 Kuo-Toa Archpriest 6 Kuo-Toas are small fish-like amphibious humanoids that used to live in coastal areas, but human settlements drove them deeper into the ground. Because of this, your party is likely to find them in isolated coastal caves or underground bodies of water. With their low stats and CR, these creatures are not a real challenge in small numbers. But their cult-like behavior and their different variants make them a real threat even to mid-level parties at higher numbers, especially now that we have more options between the low-CR Kuo-Toa and the high-CR Archpriest. 21 Sea Zombie Those Who Are Lost At Sea... Find Their Way Back Monster Challenge Rating Sea Zombie 1/4 These Waterbound creatures are to be feared for their ability to inflict disease but also sneak up on you due to their ability to move very quietly. A low armor class of 12 means they're fairly open to taking damage. Just don't attempt to deal any fire damage as it's only going to deal half the damage, but cold and electricity damage will deal double. 20 Bullywug From The Swamp To The Sea Art by Sean Murray Monster Challenge Rating Bullywug Warrior 1/4 Bullywug Bog Sage 4 Though Bullywugs are officially related to swamp areas, humanoid frogs easily fit aquatic adventures, so you have an interesting option here with the Bullywug Warrior and the sage variant for a stronger monster. They're Fey and thus escape from conditions that affect humanoids. The sage, in particular, is relatively strong thanks to their free use of Ray of Sickness. They can also make a weapon attack on the same turn. 19 Sahuagin Sea Raiders Art by David Auden Nash Monster Challenge Rating Sahuagin Warrior 1/2 Sahuagin Priest 2 Sahuagin Baron 5 A perfect option for lower levels is the Sahuagin. These underwater raiders can be quite ruthless and command sharks to do their bidding, so you can add them as minions for the battles to come. They also have an advantage against people who are hurt, so they get deadlier as the fight goes on. They can go to the surface, too, so they're not exclusively underwater (the sharks are, though). They will need to submerge after a few hours out of the water, but your players will probably not worry about their well-being.