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Plesiosaurus 5e: Stats, Hold Breath and Fighting in the Water
The plesiosaurus is a CR 2 Large beast (450 XP) with AC 13, 68 hit points, a 40-foot swim speed and a single bite with 10-foot reach: 14 damage in 2014, 11 in 2024. Its trait is Hold Breath: it can stay under for an hour, so it can wait below a boat or a dock with nobody seeing it. It doesn't grapple or drag anyone down. It's dangerous because of where you fight it. In the water the party is slow, half its weapons work badly, and the long neck reaches up onto a deck.
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Plesiosaurus Stat Block (2014)
Plesiosaurus
Large beast, unaligned
Armor Class 13 (natural armor)
Hit Points 68 (8d10+24)
Speed 20 ft., swim 40 ft.
STR
18 (+4)
DEX
15 (+2)
CON
16 (+3)
INT
2 (−4)
WIS
12 (+1)
CHA
5 (−3)
Skills Perception +3, Stealth +4
Senses passive Perception 13
Languages —
Challenge 2 (XP 450; PB +2)
Traits
Hold Breath.The plesiosaurus can hold its breath for 1 hour.
Actions
Bite.Melee Weapon Attack: +6 to hit, reach 10 ft., one target. Hit: 14 (3d6 + 4) piercing damage.
Stat block from the SRD 5.1 (2014 rules) by Wizards of the Coast, licensed under CC-BY-4.0. Check an encounter with this monster in the encounter calculator.
For a CR 2 creature it hits softly. A +6 bite hits AC 16 on a 10 or better (55%), about 7.7 damage a turn. Its 68 hit points are what make it CR 2. It takes a while to kill, and the fight happens on its ground. Stealth +4 and Perception +3 make it a decent ambusher.
The 2024 Plesiosaurus
Plesiosaurus
Large Beast (Dinosaur), Unaligned
Armor Class 13
Initiative +2 (12)
Hit Points 68 (8d10 + 24)
Speed 20 ft., swim 40 ft.
STR
18 (+4)save +4
DEX
15 (+2)save +2
CON
16 (+3)save +3
INT
2 (−4)save −4
WIS
12 (+1)save +1
CHA
5 (−3)save −3
Skills Perception +3, Stealth +4
Senses Passive Perception 13
Languages None
Challenge 2 (XP 450; PB +2)
Traits
Hold Breath.The plesiosaurus can hold its breath for 1 hour.
Stat block from the SRD 5.2.1 (2024 rules) by Wizards of the Coast, licensed under CC-BY-4.0. Check an encounter with this monster in the encounter calculator.
The only mechanical change is the bite: 11 (2d6 + 4) instead of 14 (3d6 + 4), about 6 damage a turn against AC 16. AC, HP, speeds, skills, Hold Breath and CR are identical. The 2024 type line adds the Dinosaur tag, and the stat block now lists initiative +2.
How the Plesiosaurus Fights
Strike from below, then sink. It waits submerged with an hour of air. When a boat passes, it rises, bites someone at the rail from 10 feet away, and goes back under on its next turn. Anyone wanting to hit it back has to lean over the side or get in the water.
Use its reach on the deck. A 10-foot bite means it can attack a character standing one square back from the edge without leaving the water. Characters with 5-foot weapons can't reach it without stepping to the rail.
Pick off the swimmers. A character in the water moves at half speed without a swim speed and fights with the underwater penalties below. The plesiosaurus swims at 40 feet. It goes after whoever fell in.
Leave when hurt. It's an animal. Below half its hit points, it dives and doesn't come back. With an hour of breath, nobody follows it.
How Many Plesiosaurs for a Level 3 Party?
One plesiosaurus is 450 XP. For four characters:
Party level
Encounter
2024 budget result
2014 guidelines
2
1 plesiosaurus
Moderate
Medium
3
1 plesiosaurus
Low
Easy
3
2 plesiosaurs
Moderate
Hard
4
2 plesiosaurs
Low
Medium
The 2014 column follows the 2014 Dungeon Master's Guide guidelines (used by our encounter calculator). The table assumes a fair fight. If the party is swimming, treat it as one step harder. If they're on a big ship with archers, one step easier.
For a lake fight that can actually drown people, pair it with something that grapples, like a giant octopus or a giant crocodile.
How Players Beat a Plesiosaurus
Know the underwater combat rules for your edition before anyone jumps in:
Underwater rule
2014 (SRD 5.1)
2024 (SRD 5.2.1)
Melee weapon without a swim speed
Disadvantage unless dagger, javelin, shortsword, spear or trident
Disadvantage unless the weapon deals Piercing damage
Ranged weapon
Auto-miss beyond normal range. Disadvantage within it, except crossbows, nets and thrown weapons like javelins
Auto-miss beyond normal range. Disadvantage within it
Fire
Fully immersed creatures resist fire
Anything underwater resists fire
•Stay on the boat. On deck, nobody takes underwater penalties. Ready an attack for the moment its head comes up. A polearm's 10-foot reach matches its bite.
•Avoid fire once it dives. Once it's underwater it resists fire, so save the Fireball for when it's at the surface.
Using a Plesiosaurus: Conjure Animals and Animal Shapes
Under the 2014 rules, Conjure Animals can summon one beast of CR 2 or lower. The spell says the GM has the creatures' statistics, so ask your DM before counting on a specific beast. A plesiosaurus is a good water option: a 68 HP blocker with a 10-foot reach. The 2024 Conjure Animals summons a spectral pack instead of stat-block beasts, so this doesn't apply.
Animal Shapes works in both editions (Large, CR 2). A party of plesiosaurs crosses a lake at 40 feet a round, holding breath for an hour. Polymorph works on any level 2 or higher creature. Wild Shape doesn't reach it: the SRD druid caps at CR 1, and in 2014 can't take a swimming form at all until 4th level.
Plesiosaurus Encounter Ideas
The ferry. A rope ferry crosses a deep lake. Halfway over, the rope goes slack, cut from below. The ferryman knows what's in the lake and has been paying it in fish. This week he didn't.
The flooded temple. A temple sank into a lake a century ago. The party has Water Breathing. The plesiosaurus doesn't need it for an hour at a time, and it nests in the dome.
The fisher's bargain. A fishing village feeds a plesiosaurus that keeps worse things out of their bay. A merchant wants it killed. Who's right depends on what's beyond the bay.
Frequently Asked Questions
What CR is a plesiosaurus in 5e?
The plesiosaurus is CR 2 and worth 450 XP in both the 2014 and 2024 rules.
How long can a plesiosaurus hold its breath?
One hour, in both editions. It breathes air and needs to surface after that.
Can a plesiosaurus drag you underwater?
Not by the stat block. It has a single bite with no grapple. If you want a drowning threat, add a creature that grapples, such as a giant octopus, rather than homebrewing a grapple onto the plesiosaurus.
Can you summon a plesiosaurus with Conjure Animals?
Under the 2014 rules, yes, as the one-CR-2-beast option, if your DM allows that choice. The 2024 version of the spell doesn't summon stat-block beasts.
Stat blocks: System Reference Document 5.1 (2014) and 5.2.1 (2024), Wizards of the Coast, CC-BY-4.0. Tactics, encounter math and ideas are Loreify's own.
This page includes material from the System Reference Document 5.1 and 5.2.1 by Wizards of the Coast LLC, available under the Creative Commons Attribution 4.0 International License. Loreify is not affiliated with Wizards of the Coast.