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Archelon 5e: The Giant Sea Turtle, Stats and Tactics
The archelon is a CR 4 Huge prehistoric sea turtle from the 2024 rules (SRD 5.2.1): AC 17, 90 hit points, a swim speed of 80 feet and two bites a turn at +6 for 14 damage each. It breathes air and water, hides well for something its size (Stealth +5) and crawls at 20 feet on land. It has no 2014 SRD version. Think of it as an armored tank for water encounters at levels 3 to 6: hard to hit, quick in water, and dangerous to anyone swimming next to it.
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.
AC 17 with no armor listed is the shell, and it is high for CR 4: a typical level 4 character with +5 to hit needs a 12, a 45% chance. Swim 80 feet beats a giant crocodile's 50, so almost nothing swims away from it. It has no save proficiencies: Strength +4 and Dexterity +3 are its best saves, Constitution +1 and Wisdom +2 sit in the middle, and Intelligence −3 and Charisma −2 are its weak spots.
How the Archelon Fights
Two bites, one target. Multiattack is two Bite attacks at +6. Against AC 16 each bite hits on a 10 or better (55%) for 14 piercing (3d6 + 4), which is about 15.4 damage a round. Against AC 18 it is 45% per bite, about 12.6. A level 3 wizard with around 17 hit points who ends up in the water next to an archelon is likely down in two rounds.
It owns the water. The rules make underwater fights hard on land creatures. In the 2024 rules, a creature without a Swim Speed has Disadvantage on melee weapon attacks unless the weapon deals Piercing damage, and ranged weapon attacks have Disadvantage even within normal range. A fighter with a longsword who jumps in after the turtle attacks at Disadvantage against AC 17: with +5, that hits about 20% of the time.
Ambush from below. Stealth +5 and murky water let an archelon close on a boat or a swimmer without being seen. Run its first round as a surprise bite on whoever is in the water or leaning over the rail. Its bite has only a 5-foot reach, so it has to come right up to a boat to attack someone on deck.
It doesn't fight to the death. It is a Beast with Intelligence 4. Once it's Bloodied (45 hit points or fewer), it dives and swims off at 80 feet, and nothing in the party follows it.
On land it's slow, not helpless. Walking at 20 feet, it still bites twice. A party that fights it on a beach can kite it, but a party that lets it reach the surf has given it the fight it wants.
Running an Archelon Encounter
An archelon is worth 1,100 XP. For four characters:
Party
Archelons
2024 difficulty
2014 DMG guideline
Four level 3
1
High
Hard
Four level 4
1
Moderate
Medium
Four level 5
2
Moderate
Hard
Four level 6
3
Moderate
Deadly
At level 3 one archelon uses most of a High budget (1,600 XP), and it should: a level 3 party in the water is fighting at Disadvantage. At level 5 and up one archelon is Low difficulty, so use a pair or make it part of a bigger scene. The 2014 Dungeon Master's Guide numbers come from our encounter calculator, which applies the group multiplier (×1.5 for two, ×2 for three).
The terrain matters more than the count. On a beach, an archelon is a slow brute the party can outmaneuver. In open water, with the party in a rowboat, the same encounter is a real threat.
How Players Beat an Archelon
•Stay out of the water. The best defense is a boat, a pier or a shore. Without reach, the archelon has to come to the surface next to its target to bite. The underwater combat rules talk about attacks made underwater and are silent on shooting from a deck at a surfaced turtle. DM ruling, not rules text: attacks from the boat at an archelon at the surface take no underwater penalty.
•Piercing weapons in the water. If someone has to go in, a spear, trident, rapier or shortsword avoids the 2024 underwater Disadvantage. Under the 2014 underwater rules, the exceptions are the dagger, javelin, shortsword, spear and trident.
•Spells with saves, not attacks. AC 17 shuts down attack rolls. Saving throws ignore it. Its Constitution save (+1) is the weakest of the three physical saves, and its Intelligence (−3) and Charisma (−2) saves are worse still if you have a spell that targets them; Wisdom is +2. Remember that anything underwater has Resistance to Fire damage, so Fireball on a submerged archelon deals half.
•Control the beast.Dominate Beast (Wisdom save, with Advantage if the party is fighting it) turns the archelon into a 90-hit-point ally until it breaks free (it repeats the save each time it takes damage). Before a fight starts, the 2024 Animal Friendship works on any Beast. The 2014 version fails against a beast with Intelligence 4 or higher, which includes the archelon.
•Let it leave. A Bloodied archelon is trying to leave. Letting it go saves the party resources and fits the animal.
Polymorph, Riding and Taming
Polymorph. In 2024, Polymorph turns a creature into a Beast with a CR no higher than the target's level or CR. A level 4 or higher ally can become an archelon: 90 temporary hit points, AC 17, swim 80 and two +6 bites. For an underwater adventure, that is one of the best forms a level 7 caster can pick.
Riding. It is Huge, so in the 2024 mounted combat rules any Large or smaller rider qualifies by size. DM ruling, not rules text: a broad shell counts as an appropriate anatomy, and a tamed archelon makes a good sea mount for a coastal NPC or a sahuagin raiding party.
Wild Shape. No. Even at druid level 8, Wild Shape caps at CR 1 in the 2024 rules.
Archelon Encounter Ideas
The ferry crossing. A river ferry has been losing passengers at the deepest point of the crossing. An old archelon has moved up from the delta and treats anything splashing at the surface as food. The ferryman wants it gone, and a local druid wants it guided back to the sea alive. Both jobs are fights, but only one of them ends with a dead turtle.
The nesting beach. Once a year, archelons crawl ashore to lay eggs. A merchant has hired guards to dig up the eggs for an alchemist's market. The party arrives as two archelons come out of the surf at the egg thieves. Whose side are they on?
Shell salvage. A drowned archelon's shell is worth a fortune as a boat hull or a shield wall. It lies 40 feet down in a lagoon, and its mate still guards the spot. Bring in pteranodons circling above the lagoon or a plesiosaurus in the deeper water to turn a salvage dive into a full prehistoric set piece; an ankylosaurus grazing on the beach keeps the shore from being a safe retreat.
Frequently Asked Questions
What CR is an archelon in 5e?
The archelon is CR 4, worth 1,100 XP. It is a Huge Beast (Dinosaur) in the 2024 rules (SRD 5.2.1) with AC 17 and 90 hit points.
Is the archelon in the 2014 rules?
Not in the SRD. The 2014 SRD 5.1 has no archelon, so the 2024 stat block is the only SRD version. Its stats work fine in a 2014 game.
Can an archelon breathe underwater?
Yes. Its Amphibious trait lets it breathe both air and water, so it can stay submerged as long as it likes or crawl onto a beach without any penalty.
How fast is an archelon?
It swims at 80 feet and walks at 20 feet. In water it is faster than almost any swimming character. On land, a party with a 30-foot speed can outpace it.
Can you Polymorph into an archelon?
Yes, if the target is level 4 or higher (or has a CR of 4 or higher), because Polymorph's form can't have a higher CR than the target. The target gains 90 temporary hit points in the 2024 version of the spell.
Stat blocks: System Reference Document 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.