Karkinos at the Keel
One-Shot · 6 Players · Level 10 · ~3–3.5 Hours · Single Trireme · Sacred Crab
📜 Session Summary
| Style Single-ship sea threat — Beasts → Fey parley → Sacred crab boss |
| Win Condition Drive off or defeat Karkinos (0 HP, or ≤30 HP after Coral Feast-Horn) |
| Players 6 × Level 10 · Duration 3–3.5 hrs · Board: party trireme only |
| Minis Shark (≤3), Octopus (1), Sea spirit (≤5), Sea/Water Nymph (1), Dolphin (1), Cancer the Crab (1) |
| Setting Open Aegean — Misthaven fog, a single party trireme running under oars in glassy water, blood-chum trail ahead of the bow, and the deep rising toward the hull; no port, no anchor, no second ship — just ninety feet of pine and bronze between the party and the sacred crab's hunger. |
| Atmosphere Claustrophobic maritime dread modulated by Fey grace — the sea is alive and opinionated; the crab is sacred, not evil; the wrongness is in the poachers' blood-chum that broke the natural covenant, not in Poseidon's creature. |
| Materials Tarred rope, bronze oar-locks, salt-bleached pine, coral trumpet warm in the hand, pearl-net tangled on the ram, seawater everywhere. |
| Tone Tight, physical, mythic — the trireme is both stage and weapon; Karkinos should feel Huge before it arrives; the Horn should feel like the right answer even before the party knows what it does. |
Description
The fog parts alongside the bow rail and a Nereid herald steps onto the deck without getting the planking wet. She places the Coral Feast-Horn on the rail and tells the party that poachers used a false Poseidon feast-horn two nights ago to draw sea-life into a killing cove. Most of the blood-chum ran south. Some of it ran under this keel. Karkinos, a sacred crab older than the current dynasty, has followed the blood-trail to its source. He is not attacking out of malice — he is a hunger that was misdirected and cannot remember how to stop. The true Horn can redirect that hunger. The party has until the crab reaches the hull.
The Coral Feast-Horn is small enough to fit in one hand and warm to the touch in a way that doesn't make sense given the sea air. It pulses faintly with each wave. When blown, it produces a sound that bypasses the ears entirely and lands somewhere behind the sternum — the kind of sound that makes a swimming creature turn toward open water. Blowing it near Karkinos at the right moment is the cleanest path through this fight. The Nereid herald says it works once, fully, in the final confrontation. Before that, each blow turns a single creature aside for a round.
The oar-wash at the hull is already stained. Sharks circle the ram. The octopus found the oar-ports forty minutes ago and has been testing them since. The crew is below decks because the mate made the right call. The party has the whole deck to themselves, the fog, the blood-smell, and ninety feet of pine between them and what's coming from the deep.
DM — Coral Feast-Horn Payoffs Across Acts: Enc. 1: blow near circling sharks (DC 13 WIS or end next turn moving away from hull — 1/short rest). Enc. 2: blow when Thalassa rises — she recognizes it immediately as the true horn, DC drops to 10 for the parley resolution, and she stops being actively hostile before a word is spoken. Enc. 3: blow adjacent to Karkinos or at the bow rail — DC 15 WIS or Karkinos is incapacitated 1 round, loses legendary actions that round, soft underbelly exposed (attacks Advantage until it moves). At ≤30 HP after this blow: it plunges away permanently.
Trireme Map (Single Ship)
Main deck 40×50 ft · raised bow +15 ft · raised stern +25 ft · 90 ft total length (tapered ends) · center mast/sail · 15 ft ram at bow. No second ship — water, sky, and creatures only. Place shark/octopus minis in water adjacent to hull; Karkinos climbs the ram or stern in Enc. 3.
Major Beats
- The Herald Arrives. Steps onto the deck from the fog — no spray, no sound, just present. Knows the party by their ship, not their names. Investigation DC 14: the Horn is older than Poseidon's cult, from a covenant that predates the Olympian order. Insight DC 15: she is afraid of what Karkinos will become if this escalates further than one ship.
- Enc. 1 — The Oar-Wash. Sharks first, then the octopus reveals itself at the oar-ports. Crew chief shouts from below (DC 13 Perception) that three oar-banks can still row — but not for long. Every oar-bank destroyed past 2 means Karkinos gains +10 ft move in Enc. 3 per lost bank — the ship cannot maneuver away from its approach lane.
- Enc. 2 — Thalassa's Arrival. Angry — performing anger at someone and the party is present. Insight DC 14: not angry at them specifically. DC 17: she recognizes the true Horn before it's shown — expression changes when a PC reaches for it. RP Hook: she answers one question about Karkinos's habits if respected, not commanded. Ask right and she reveals the mast-targeting behavior.
- Enc. 3 — Karkinos Climbs. Shadow falls across the ram before its claws do. Two Legendary Actions before it fully boards. It targets the mast first — associates that silhouette with the poacher ship. The party can exploit this: use the mast as bait to control positioning. Horn payoff window opens at ≤50% HP.
Session Rewards
Keepable prizes earned by completing (or excelling at) this session. One character claims each reward unless noted. Full cards are under Reward Cards.
| Reward | Description | Criteria |
|---|---|---|
| Coral Feast-Horn | Coral trumpet that turns sea-hunger aside from your ship. | Sound the true feast and calm Poseidon's sacred crab without dooming the hull. |
Creature / Enemy List
| Creature | Easy | Med | Hard | Notes |
|---|---|---|---|---|
| Hunting Shark | 2 | 3 | 3 | Enc. 1 |
| Giant Octopus | 0 | 1 | 1 | Enc. 1 |
| Thalassa | — | 1 | 1 | Enc. 2 recruit |
| Sea Spirit | 0–2 | 0–3 | 0–5 | Optional |
| Karkinos | 1 adj | 1 | 1 | Boss |
Encounter 1 — Blood in the Oar-Wash
Overview
Blood-chum from the poacher trail has brought three Hunting Sharks to the ram and a Giant Octopus to the oar-ports. The sharks are Blood Frenzy-primed — any creature missing HP draws their immediate attention. The octopus is methodical: it has been probing the oar-banks for structural weakness since before the party boarded. The crew is below; the deck is clear. Win condition: clear the beasts with at least 2 of 4 oar-bank zones intact.
🗺 Terrain
Single trireme (90 ft): Main deck 40×50 ft, raised bow +15 ft, raised stern +25 ft. Oar-ports along both sides (octopus reaches through, AC 12/HP 12 each). Ram 15 ft ahead of bow (sharks circle here, elevated perspective from bow). Water ring 15 ft around hull (sharks have OA on exit). Mast and rigging: Climb DC 13 Athletics to reach the boom — grants Advantage on ranged attacks into water. Mooring ring: DC 12 Athletics to secure a rope to pull a fallen PC back aboard (vs. DC 14 sharks pulling the other way).
Non-Combat Options
- Path A — Coral Feast-Horn (Shark Dispersal): Blow the Horn while standing at the bow rail (Action; 1/short rest). Sharks within 30 ft make DC 13 WIS save or end their next turn moving away from the hull. Combined with a group Animal Handling/Religion challenge (3 successes before 3 failures at DC 13) — success drives all three sharks off the encounter without combat. Octopus is unaffected by the Horn (it doesn't hear above water) — must be dealt with separately.
- Path B — Cut the Octopus Grapple: The octopus holds one oar-bank in each of its first two rounds — it is not attacking PCs directly unless a PC enters the water. Dealing 15 damage to the tentacle section (treated as object AC 10) or succeeding DC 14 Athletics while adjacent to the oar-port (1 round) forces it to release and move off. Create Water / Gust of Wind into an oar-port dislodges it without damage (DC 11 CON save for the octopus; failure = moves off 1d4+1 rounds). This preserves both oar-banks and avoids a full combat round.
- Path C — Chum Redirect: The poachers' blood-chum trail runs south. A PC can throw a bucket of salted fish-blood (found in the galley, DC 11 Investigation to locate quickly) 30 ft south of the hull — sharks follow blood trails. DC 14 Survival to read the current and throw correctly. On success, 1d3 sharks divert south for 2 rounds (removing them from the encounter temporarily while the octopus is handled).
Mechanics
- Oar banks: 4 zones (AC 12 / HP 12). If ≥3 destroyed → Short Rest only before Enc. 2; else Long Rest. Each lost bank beyond 2 gives Karkinos +10 ft speed in Enc. 3 (it can pursue the ship rather than needing to be navigated toward).
- Blood Frenzy: Sharks have Advantage on attacks vs. any creature below max HP. If a PC goes overboard: sharks get OA on entry; Athletics DC 12 to climb ram/oar-ports; each round in water with missing HP attracts 1 additional shark attention.
- Octopus Ink Cloud (Recharge 4–6): 20-ft radius heavily obscured underwater for 1 minute — note this only matters for creatures in the water, but it can blind a PC who jumps in voluntarily.
Creature Cards
Hunting Shark
Large Beast, Unaligned · CR 2 · Mini ×3
AC 12 | HP 45 (6d10+12) | Speed 0 ft., swim 40 ft.
Senses: blindsight 30 ft. · Blood Frenzy: adv vs. creatures missing HP
Hull Circler. Can make opportunity attacks against creatures that leave the water within 5 ft. of the hull or ram.
Bite. +6 to hit. Hit: 13 (2d8+4) piercing.
Giant Octopus
Large Beast, Unaligned · CR 1 · Mini ×1
AC 11 | HP 52 (8d10+8) | Speed 10 ft., swim 60 ft.
Skills: Stealth +5 · Hold Breath 1 hour on land
Oar Grapple. While grappling the hull/oars, the ship’s row Speed is 0 until freed (Athletics DC 14 as action, or deal 15 damage to tentacles treated as object AC 10).
Tentacles. +5 to hit, reach 15 ft. Hit: 10 (2d6+3) bludgeoning + grapple (escape DC 16).
Ink Cloud (Recharge 4–6). 20-ft radius underwater heavily obscured 1 minute.
Coral Feast-Horn
Wondrous Item (maguffin), Unique
Appearance: small coral trumpet, warm and faintly pulsing
Handout (22 words). "When the sacred crab climbs for blood that is not the sea’s, sound this horn — hunger hears the true feast."
Enc. 1–2. Action: blow once (1/short rest) — sharks or octopus within 30 ft. make a DC 13 Wisdom save or end their next turn moving away from the hull.
Enc. 3. Action adjacent to Karkinos or at the bow rail: sound the true feast (once). Karkinos must succeed DC 15 Wisdom or be incapacitated until end of its next turn and lose Legendary Actions that round; soft underbelly exposed (attacks vs. it have advantage until it moves).
Encounter 2 — The Nymph’s Shoal
Overview
Thalassa rises with 3× Sea Spirits. She is angry and performing it — the poachers used a false Nereid artifact, and her shoal found three fish dead in the blood-chum who should not be. The party has the true Horn; showing it changes her tone before she speaks a second sentence. The pearl-net from the poacher haul is tangled on the ram. She is watching for whether the party is the kind of people who notice things that belong to someone else. Peaceful resolution → Thalassa aids Enc. 3; Delphinus arrives as omen of Poseidon's patience.
🗺 Terrain
Still water around the hull; light fog (lightly obscured 30 ft radius). No second ship. Sea Spirits are in the water adjacent to the hull on all sides — they can move onto the deck (climb 5 ft) or dive below. Thalassa stands on the water surface (no terrain restriction). Pearl-net tangled on the ram (DC 12 Investigation on ram, DC 10 with a 60-second search).
Non-Combat Options
- Path A — Show the True Horn: If a PC reaches for the Coral Feast-Horn while Thalassa is speaking (no roll — just a visible action), her expression changes immediately. She stops mid-sentence. Insight DC 12: she recognizes it. This immediately drops any Persuasion/Religion DC by 4 (to DC 10) and removes her angry-performance stance. She will not attack if the Horn is shown before she finishes her opening demand.
- Path B — Return the Pearl-Net: Locate the pearl-net on the ram (DC 12 Investigation, or 60-second search without a roll). Returning it to Thalassa (no check) grants one free automatic success on any one subsequent Enc. 3 roll of the party's choice, and she answers 2 questions about Karkinos's habits (including the mast-targeting behavior and the soft underbelly location). This is in addition to the standard recruitment — it is a gift that earns something beyond alliance.
- Path C — Recruit a Sea Spirit as Scout: If Thalassa is calmed but before she is formally recruited, a PC can appeal to a Sea Spirit directly (DC 12 Persuasion — they are Chaotic Neutral and curious). On success: the spirit agrees to warn when Karkinos surfaces in Enc. 3 — the party cannot be surprised and Karkinos's first approach is from a known direction (removes its opening Legendary Action ambush capability).
Mechanics
- Non-combat primary path: Show Horn + Persuasion/Religion DC 14 (DC 10 with pearl-net returned, DC 10 with Horn shown first). Insight DC 12 grants Advantage on first Persuasion.
- Combat path (if party attacks first or refuses to engage): Thalassa + spirits for 2 rounds or until she hits ½ HP, then withdraws. No Enc. 3 ally. Sea Spirits do not pursue — they're curious, not vengeful.
- Recruitment: Peaceful resolution → Thalassa joins Enc. 3: casts healing word once (2d4+4 HP), can use Help to expose Karkinos's soft underbelly (target becomes next attack Advantage). Delphinus arrives: Rescue Breach (reaction when PC falls overboard, DC 10 Athletics to reboard).
Creature Cards
Thalassa (Sea Nymph)
Medium Fey, Neutral · CR 3 · Mini: Sea/Water Nymph ×1
AC 14 | HP 58 (9d8+18) | Speed 30 ft., swim 40 ft.
Spell DC 14 · fog cloud, control water (1/day), healing word
RECRUITMENT. Spare her shoal / return a stolen pearl-net (skill path) → she joins Enc. 3: once casts healing word and can use Help to expose Karkinos’s underbelly.
Anger Path. If the party attacks first, she fights 2 rounds then flees; no ally in Enc. 3.
Multiattack. Two tidal darts.
Tidal Dart. +5 to hit, range 60 ft. Hit: 8 (1d8+3) bludgeoning + shove 5 ft.
Charming Glance (1/day). One creature DC 14 Wisdom or charmed 1 minute.
Sea Spirit (Lesser Nereid)
Medium Fey, Chaotic Neutral · CR 1/2 · Mini ×5
AC 12 | HP 22 (5d8) | Speed 30 ft., swim 30 ft.
Optional fog clutter / messengers
Mist Form. Bonus action Hide while lightly obscured by spray.
RECRUITMENT. If not attacked: Persuasion DC 12 → one spirit warns when Karkinos will surface (party cannot be surprised in Enc. 3).
Salt Slap. +4 to hit. Hit: 5 (1d6+2) bludgeoning.
Delphinus (Dolphin Ally)
Medium Beast, Neutral Good · CR 1/2 · Mini ×1
AC 12 | HP 27 | Speed 0 ft., swim 60 ft.
Poseidon’s omen — appears if Thalassa is recruited or horn blown in Enc. 2
Rescue Breach. Reaction: when a PC falls overboard within 20 ft., Delphinus moves and the PC may board as part of that reaction (Ath DC 10).
Ram. +4 to hit. Hit: 7 (1d8+2) bludgeoning.
Encounter 3 — Karkinos Climbs (Boss)
Overview
Karkinos heaves onto the bow via the 15 ft ram — its shadow appears before its claws do. It uses two Legendary Actions before fully boarding: one Detect (fixing every creature's position), one Claw (testing the ram-housing). It targets the mast on its first full turn (associating the silhouette with the poacher ship). Parties who know this (from Thalassa's intel) can lure it to one side of the deck and control positioning. Optional: 1 shark remains in water (Enc. 1 leftover — Blood Frenzy against any overboard PC).
APL 10 — Deadly encounter (≈16,800 XP threshold for 6×L10). Karkinos CR 9 (5,000 XP) staged. For APL10 Deadly: apply elite HP (+40 HP → 208 total), add a second Legendary Resistance (total 2/day), and the Deck Slam becomes Recharge 4–6 instead of at-will. Effective XP with terrain/siege multiplier ≈ 11,000 XP → Deadly for this tier. Thalassa's absence (if not recruited) makes this a significantly harder fight: no healing word, no underbelly exposure.
🗺 Terrain
Full 90 ft deck: Ram (15 ft extension, difficult terrain, Karkinos entry lane — Siege Monster doubles its damage to ram housing). Mast/boom (20 ft height, climb DC 13 — Karkinos can strike the base to topple: AC 14/HP 30, toppled mast creates difficult terrain 20 ft radius + DC 14 Dex or 2d8 bludgeoning). Stern rail (raised 25 ft — if Karkinos reaches stern, it can launch Deck Slam from elevation: increase radius to 15 ft). Overboard zone (water, 1 remaining shark — DC 12 Athletics to reboard; Delphinus assists if recruited). Oar-bank status: Each destroyed bank (from Enc. 1) means Karkinos can't be maneuvered away from — it approaches from the undamaged-oar side.
Non-Combat Options
- Path A — Coral Feast-Horn (Preferred Win at ≤30 HP): Blow the Horn adjacent to Karkinos or at the bow rail when it is at ≤50% HP (ideally ≤30 HP): DC 15 WIS or Karkinos is incapacitated 1 round, loses legendary actions that round, soft underbelly exposed (all attacks Advantage until it moves). At ≤30 HP after this blow: it plunges permanently away — Poseidon's sacred covenant reasserts itself. This is the preferred win: the crab survives, the sea remains in proper order.
- Path B — Mast Bait (Positioning Control): If the party knows Karkinos targets the mast first (Thalassa intel or DC 15 Perception in Round 1), a PC can deliberately stand at the mast base (drawing its attention) while others flank. Two flanking PCs gain Advantage on attacks that round; the PC at the mast draws a Claw attack but controls where Karkinos moves. This is how to get it away from the oar-bank damage zone.
- Path C — Soft Underbelly Exposure: Without the Horn, a party can expose the underbelly manually: Prone or Restrained Karkinos (DC 16 STR save to Restrain via Pincer Crush — use its own mechanic against it; or a Tanglefoot Bag / Web spell). While prone/restrained: AC drops to 15, attacks have Advantage. Thalassa can also Help to expose it once (if recruited).
Mechanics
- Win condition: 0 HP or ≤30 HP after a successful Coral Feast-Horn blow this fight (plunges away).
- Deck Slam (at-will, base — upgraded to Recharge 4–6 at APL10 elite): each creature in 10-ft radius on deck DC 16 Dex or 14 (4d6) bludgeoning and prone. Karkinos prefers to use this in the center of the deck to split the party.
- Overboard: Athletics DC 12 to reboard without Delphinus. With Delphinus: DC 10. Remaining shark: Blood Frenzy vs. overboard PC with missing HP.
- Persistence: killing Karkinos is allowed but Nereids mourn. Party that uses the Horn correctly (preferred win) receives Thalassa's blessing before she departs — Advantage on one Wisdom saving throw each within the next 7 days.
Creature Cards
Karkinos, Sacred Crab of Poseidon
Huge Monstrosity, Neutral · CR 9 · BOSS · Mini: Cancer the Crab
AC 18 (natural) | HP 168 (16d12+64) | Speed 30 ft., swim 40 ft., climb 20 ft.
Saves: Str +10, Con +8 · Resist: bludgeoning nonmagical · LR 2/day
Climb Hull. Treat the trireme as climbable terrain; can end turns on main/bow/stern decks.
Siege Monster. Double damage to objects (rails, mast step, ram housing).
Soft Underbelly. While prone, restrained, or after Coral Feast-Horn success: attacks have advantage; its AC is 15 until start of its next turn.
Persistence. Sacred beast — driving it off at ≤30 HP with the Horn counts as victory; killing it is allowed but Nereids mourn.
Multiattack. Two claws. If both hit the same target, it is grappled (escape DC 16).
Claw. +10 to hit, reach 10 ft. Hit: 16 (2d8+6) bludgeoning.
Pincer Crush (Recharge 5–6). One grappled creature DC 16 Strength or 22 (4d8+4) bludgeoning and restrained while grappled.
Deck Slam. Each creature in a 10-ft radius on deck Dex DC 16 or 14 (4d6) bludgeoning and prone.
Detect (1). Wisdom (Perception) check.
Claw (1). One claw attack.
Scuttle (2). Move up to half speed without provoking; may climb.
Coral Feast-Horn
Wondrous Item (maguffin), Unique
Appearance: small coral trumpet, warm and faintly pulsing
Handout (22 words). "When the sacred crab climbs for blood that is not the sea’s, sound this horn — hunger hears the true feast."
Enc. 1–2. Action: blow once (1/short rest) — sharks or octopus within 30 ft. make a DC 13 Wisdom save or end their next turn moving away from the hull.
Enc. 3. Action adjacent to Karkinos or at the bow rail: sound the true feast (once). Karkinos must succeed DC 15 Wisdom or be incapacitated until end of its next turn and lose Legendary Actions that round; soft underbelly exposed (attacks vs. it have advantage until it moves).
Thalassa (Sea Nymph)
Medium Fey, Neutral · CR 3 · Mini: Sea/Water Nymph ×1
AC 14 | HP 58 (9d8+18) | Speed 30 ft., swim 40 ft.
Spell DC 14 · fog cloud, control water (1/day), healing word
RECRUITMENT. Spare her shoal / return a stolen pearl-net (skill path) → she joins Enc. 3: once casts healing word and can use Help to expose Karkinos’s underbelly.
Anger Path. If the party attacks first, she fights 2 rounds then flees; no ally in Enc. 3.
Multiattack. Two tidal darts.
Tidal Dart. +5 to hit, range 60 ft. Hit: 8 (1d8+3) bludgeoning + shove 5 ft.
Charming Glance (1/day). One creature DC 14 Wisdom or charmed 1 minute.
⚖️ Difficulty Scaling
As Written ★ — 6 Players, Average Level 10
- Baseline for this guide. Encounter 1–2 are Hard; the final encounter is Deadly for six PCs at average level 10.
- XP budgets (6×L10 thresholds): Hard ≈ 10,800 · Deadly ≈ 16,800. Prefer adding elite pressure, legendary actions, or terrain danger over bloating minion counts past the choke.
Library Standard — 6 Players, Average Level 8
- Dial back: reduce boss HP ~20–25%; cut one legendary action option or recharge breath to 6 only; Favor/track thresholds −1 where present; skill DCs −1; drop one minion wave or −2 CR1–2 creatures from Hard openers.
Easier
- APL 8–9: use the Library Standard (6×L8) box, then shave one more minion wave or remove one recharge ability.
Harder
- APL 11–12: boss HP +20%; +1 legendary; final encounter gains one extra elite or lair pulse; skill DCs +1.
📋 Appendix — Cards
Nereid Herald (Quest Giver)
Medium Fey, Neutral Good · Quest Giver
Public face: salt-crowned messenger stepping from the mist onto the deck
Motivation. A sacred crab of Poseidon — Karkinos — has been goaded from the deep by poachers’ blood-chum. Calm or defeat it before it cracks the next hull.
Secret. The poachers used a false “feast-horn” of Poseidon; the true Coral Feast-Horn reverses the frenzy.
Coral Feast-Horn
Wondrous Item (maguffin), Unique
Appearance: small coral trumpet, warm and faintly pulsing
Handout (22 words). "When the sacred crab climbs for blood that is not the sea’s, sound this horn — hunger hears the true feast."
Enc. 1–2. Action: blow once (1/short rest) — sharks or octopus within 30 ft. make a DC 13 Wisdom save or end their next turn moving away from the hull.
Enc. 3. Action adjacent to Karkinos or at the bow rail: sound the true feast (once). Karkinos must succeed DC 15 Wisdom or be incapacitated until end of its next turn and lose Legendary Actions that round; soft underbelly exposed (attacks vs. it have advantage until it moves).
Hunting Shark
Large Beast, Unaligned · CR 2 · Mini ×3
AC 12 | HP 45 (6d10+12) | Speed 0 ft., swim 40 ft.
Senses: blindsight 30 ft. · Blood Frenzy: adv vs. creatures missing HP
Hull Circler. Can make opportunity attacks against creatures that leave the water within 5 ft. of the hull or ram.
Bite. +6 to hit. Hit: 13 (2d8+4) piercing.
Giant Octopus
Large Beast, Unaligned · CR 1 · Mini ×1
AC 11 | HP 52 (8d10+8) | Speed 10 ft., swim 60 ft.
Skills: Stealth +5 · Hold Breath 1 hour on land
Oar Grapple. While grappling the hull/oars, the ship’s row Speed is 0 until freed (Athletics DC 14 as action, or deal 15 damage to tentacles treated as object AC 10).
Tentacles. +5 to hit, reach 15 ft. Hit: 10 (2d6+3) bludgeoning + grapple (escape DC 16).
Ink Cloud (Recharge 4–6). 20-ft radius underwater heavily obscured 1 minute.
Sea Spirit (Lesser Nereid)
Medium Fey, Chaotic Neutral · CR 1/2 · Mini ×5
AC 12 | HP 22 (5d8) | Speed 30 ft., swim 30 ft.
Optional fog clutter / messengers
Mist Form. Bonus action Hide while lightly obscured by spray.
RECRUITMENT. If not attacked: Persuasion DC 12 → one spirit warns when Karkinos will surface (party cannot be surprised in Enc. 3).
Salt Slap. +4 to hit. Hit: 5 (1d6+2) bludgeoning.
Thalassa (Sea Nymph)
Medium Fey, Neutral · CR 3 · Mini: Sea/Water Nymph ×1
AC 14 | HP 58 (9d8+18) | Speed 30 ft., swim 40 ft.
Spell DC 14 · fog cloud, control water (1/day), healing word
RECRUITMENT. Spare her shoal / return a stolen pearl-net (skill path) → she joins Enc. 3: once casts healing word and can use Help to expose Karkinos’s underbelly.
Anger Path. If the party attacks first, she fights 2 rounds then flees; no ally in Enc. 3.
Multiattack. Two tidal darts.
Tidal Dart. +5 to hit, range 60 ft. Hit: 8 (1d8+3) bludgeoning + shove 5 ft.
Charming Glance (1/day). One creature DC 14 Wisdom or charmed 1 minute.
Delphinus (Dolphin Ally)
Medium Beast, Neutral Good · CR 1/2 · Mini ×1
AC 12 | HP 27 | Speed 0 ft., swim 60 ft.
Poseidon’s omen — appears if Thalassa is recruited or horn blown in Enc. 2
Rescue Breach. Reaction: when a PC falls overboard within 20 ft., Delphinus moves and the PC may board as part of that reaction (Ath DC 10).
Ram. +4 to hit. Hit: 7 (1d8+2) bludgeoning.
Karkinos, Sacred Crab of Poseidon
Huge Monstrosity, Neutral · CR 9 · BOSS · Mini: Cancer the Crab
AC 18 (natural) | HP 168 (16d12+64) | Speed 30 ft., swim 40 ft., climb 20 ft.
Saves: Str +10, Con +8 · Resist: bludgeoning nonmagical · LR 2/day
Climb Hull. Treat the trireme as climbable terrain; can end turns on main/bow/stern decks.
Siege Monster. Double damage to objects (rails, mast step, ram housing).
Soft Underbelly. While prone, restrained, or after Coral Feast-Horn success: attacks have advantage; its AC is 15 until start of its next turn.
Persistence. Sacred beast — driving it off at ≤30 HP with the Horn counts as victory; killing it is allowed but Nereids mourn.
Multiattack. Two claws. If both hit the same target, it is grappled (escape DC 16).
Claw. +10 to hit, reach 10 ft. Hit: 16 (2d8+6) bludgeoning.
Pincer Crush (Recharge 5–6). One grappled creature DC 16 Strength or 22 (4d8+4) bludgeoning and restrained while grappled.
Deck Slam. Each creature in a 10-ft radius on deck Dex DC 16 or 14 (4d6) bludgeoning and prone.
Detect (1). Wisdom (Perception) check.
Claw (1). One claw attack.
Scuttle (2). Move up to half speed without provoking; may climb.
Reward Cards
Post-session keepables. Reward is the first tag. Mechanics below are for ongoing use after this oneshot.
Coral Feast-Horn
Reward · Wondrous · 1/Short Rest
Mechanics. Once per short rest, as an action, blow the horn. Each shark, crab, octopus, or other beast with a swimming speed within 30 feet must succeed on a DC 13 Wisdom saving throw or spend its next turn moving away from you by the safest route. Once per long rest, as an action, one Huge or larger aquatic monstrosity or beast within 30 feet must succeed on a DC 15 Wisdom saving throw or be incapacitated until the end of its next turn.
Appearance. A small coral trumpet, warm and faintly pulsing like a living heart.
Lore. Poseidon's feast-call, kept by the crew who reminded Karkinos what blood belongs to the sea.
Quote. "When the sacred crab climbs for blood that is not the sea's, sound this horn." — Feast-Horn
Earn when: Sound the true feast and calm Poseidon's sacred crab without dooming the hull.