Cetus
Cetus — The Encounter
The fanged sea-doom Perseus slew to free Andromeda · a boss your table can run with almost no prep. SRD 5.1-compatible.
Who Is Cetus
When the old kingdoms grew proud and hung their daughters' beauty above the sea's own, the deep answered with Cetus. No demon and no god, only the ocean's appetite given scale and tooth — a length of cold muscle that rose where coastlines forgot to fear. Sailors say it does not hunt so much as collect: it takes what is offered and what is not, swallowing the boastful whole and leaving the humble to row home and warn the rest. The hero Perseus is named its bane, having shown the beast its own reflection in a severed gaze and turned its fury to stone. Yet stories of stone seldom hold; the tide returns what it pleases. Where the water glows an unnatural blue and the chained are set upon the rocks as toll, Cetus is already coiling below, listening for the splash of a tribute that will never be enough.
Run Cetus in Sixty Seconds
- Hold for the surface. Don't roll initiative until Cetus breaches — that triggers Dread of the Deep (DC by tier) and frightens the whole shoreline at once.
- Open with Bite-grapple, then Swallow. Lock the lowest-AC target turn one, swallow it turn two, then dive away from the rest of the melee.
- Kill-priority: the swallowed PC. Whoever is inside takes acid every turn and is the table's clock — the party must deal 20 in a turn to force a regurgitate, so make them choose between rescue and damage.
- When bloodied (67 HP), go pelagic. Stop trading blows; use Sounding Dive and swim moves to drag the fight into deep water where blindsight and swim 60 ft. let it pick targets at will.
- Three ways to run it: solo leviathan boss for 5 mid PCs; the centerpiece a school of aquatic adds feed toward; or a chained 'Bound' scion a sea-witch villain commands.
Cetus
Huge monstrosity, neutral evil
CR 6 · 2,300 XP · GUIDELINEHold Breath. Cetus can hold its breath for 1 hour, and it suffers no penalty for fighting at any ocean depth.
Dread of the Deep. Signature. When Cetus surfaces or is first seen, each creature within 60 ft. that can see it must succeed on a DC 14 Wisdom saving throw or be frightened until the end of its next turn. A frightened creature that ends its turn unable to see Cetus repeats the save. A creature that succeeds is immune to this trait for 24 hours.
Actions
Multiattack. Cetus makes one Bite attack and one Tail Slam attack. It can use Swallow in place of the Bite.
Bite. Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit: 22 (3d10 + 5) piercing damage, and the target is grappled (escape DC 15) if it is a Large or smaller creature.
Tail Slam. Melee Weapon Attack: +7 to hit, reach 15 ft., one target. Hit: 16 (2d8 + 5) bludgeoning damage, and the target must succeed on a DC 15 Strength saving throw or be knocked prone.
Swallow. Cetus makes one Bite attack against a Large or smaller creature it is grappling. On a hit, the target is swallowed and the grapple ends. A swallowed creature is blinded and restrained, has total cover against attacks from outside, and takes 10 (3d6) acid damage at the start of each of Cetus's turns. If Cetus takes 20 damage or more on a single turn from a swallowed creature, it must succeed on a DC 14 Constitution save at the end of that turn or regurgitate the creature, which falls prone within 10 ft. If Cetus dies, a swallowed creature can escape using 15 ft. of movement, exiting prone.
Legendary Actions (3/Round)
Detect. Cetus makes a Wisdom (Perception) check.
Tail Slam. Cetus makes one Tail Slam attack.
Sounding Dive (Costs 2 Actions). Cetus moves up to its swim speed without provoking opportunity attacks, then each creature within 10 ft. of where it surfaces or submerges takes 9 (2d8) bludgeoning damage from the churning swell (DC 15 Dexterity save halves).
A sinuous leviathan of scale and fin, its needle-toothed maw gaping wide as it heaves up from a glowing tide over jagged sea-stones. Spined frills fan from its serpentine body like drowned wings.
Cetus, Bound
Companion · acts on your initiative
Bound · GUIDELINETide-Bound (signature). While within 30 ft. of a body of water, the Bound Cetus has advantage on attack rolls against any creature that is grappled or prone.
Actions
Rending Bite. Melee Weapon Attack: +6 to hit, reach 10 ft., one target. Hit: 17 (3d8 + 4) piercing damage; a Medium or smaller target is grappled (escape DC 14).
Reactions
Undertow. When a creature within 10 ft. that the Bound Cetus can see is hit by an ally, it may drag that creature up to 10 ft. through water, ending the move with the creature prone.
A lesser scion of the sea-doom, chained to a summoner's will by salt-rite and offering — loyal only so long as the tribute keeps coming.
Guideline numbers — formula-tuned and read from the miniature's design, not yet table-proven. Tell us how it ran in the comments.
How It Fights — by Tier
Same creature, scaled threat. The traits never change; only the numbers move.
Open by surfacing for Dread of the Deep, then Bite-and-grapple the nearest squishy target to start dragging it under. If the party clusters on a pier or boat, lead with Tail Slam to scatter and prone them. Kill-priority is anyone who has been swallowed — finish them before the table can free them.
Surface for Dread of the Deep, Bite the lowest-AC target, then Swallow it next turn and dive away from the melee. Spend legendary actions on Tail Slam against casters and Sounding Dive when 2+ heroes bunch at the water's edge. As a solo boss this is a full encounter for 5 mid-level PCs; otherwise pair it as the centerpiece a smaller school of sahuagin-style adds feed toward.
Same play, scaled up: surface, frighten, Bite-Swallow, dive. Use Sounding Dive to wreck clustered melee and legendary Tail Slams to keep ranged threats prone in the surf. Kill-priority is the swallowed PC; keep diving so the party must chase into deep water where Cetus owns the field.
Put Cetus on the table
Download the presupported STL and run the fight tonight — the model, and the encounter that comes with it.
Get the STL on MyMiniFactory →Clay Cyanide Companion Rules v1
How a bound creature acts
- A companion acts on its owner's initiative, immediately after the owner.
- It uses the Companion block above — roughly ×0.6 HP and damage, no recharge abilities, and at most one reaction trait.
- It moves freely; it takes its Action only while its owner is conscious.
- At 0 HP a companion is broken, not dead — restored on a long rest unless your table rules otherwise.
Original Clay Cyanide material © Clay Cyanide LLC — explicitly not the non-SRD official sidekick rules.
Questions, Asked at the Table
What CR is Cetus?
Native CR 6 (2,300 XP), a Tier 2 boss built for levels 5-10. It is solo_capable: with legendary actions and Swallow it can carry a whole encounter for a party of five. Drop to the level 1-4 column or climb to the 11-15 column using the tiers table — traits stay identical, only AC, HP, to-hit and DCs move.
Can Cetus be a companion or ally?
Yes — as 'Cetus, Bound,' a lesser scion chained to a summoner by salt-rite (AC 14, 80 HP). It grapples and drags with Rending Bite, gains advantage near water against grappled or prone foes, and uses its Undertow reaction to haul a struck enemy through the surf and leave it prone. It serves only while the tribute keeps coming.
Is Cetus a public-domain creature?
Entirely. Cetus is the sea-monster of Greek myth set against Andromeda and slain by Perseus, attested in Ovid and classical sources well in the public domain. This stat block uses only SRD 5.1 mechanics and frames the beast through that mythology — no proprietary cosmology or product identity.
Tell Us How It Ran
This work includes material taken from the System Reference Document 5.1 ("SRD 5.1") by Wizards of the Coast LLC and available at dnd.wizards.com/resources/systems-reference-document. The SRD 5.1 is licensed under the Creative Commons Attribution 4.0 International License available at creativecommons.org/licenses/by/4.0/legalcode.
Clay Cyanide Miniatures is not affiliated with, endorsed, sponsored, or specifically approved by Wizards of the Coast LLC. This content is compatible with the fifth edition of the world's most popular fantasy roleplaying game. Companion rules, lore, names, and original mechanics © Clay Cyanide LLC.
Technical Specifications
32mm, 75mm
STL, Pre-supported STL
Standard or ABS-like resin, 0.05mm layer height
Yes — ready to print, optimized supports included
Played Cetus at your table? Log in with your Obsidian Tavern account to leave a balance note, a war story, or a file issue — the sharpest reports get the block revised.
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