Cancer
Cancer — The Encounter
The Crab-Armored Sentinel, Karkinos enthroned beneath the summer stars · a boss your table can run with almost no prep. SRD 5.1-compatible.
Who Is Cancer
When Karkinos, the great crab, was crushed beneath the heel of a hero, the gods could not bear to waste so faithful a servant and hung it among the stars as the sign of Cancer. From that constellation the Colony descends: warrior-sentinels grown half into their own shells, each one a node of the zodiac's tide. The Crab-Armored Sentinel is no wanderer. She is set, like a stone in a wall, before a threshold or a holy stair, and there she remains while moons rise and fall. Her body answers the pull of unseen waters, hardening when she stands her ground and softening only when she is forced to give it. The faithful carve her glyph into boundary-stones, believing that where her sign is cut, nothing crosses without her leave. Soldiers who break her ranks tell of claws closing in the dark and of a cold that creeps in with the tide, slow, patient, and impossible to outwait.
Run Cancer in Sixty Seconds
- She is a wall, not a hunter. The Sentinel wants to stand on one 10-foot space and never leave it; the whole fight is built around that. Set her in a doorway, stair, or bridge.
- Open with a grapple. Hit the strongest melee PC with both pincers to grapple (escape DC 15), pinning them in her threatened space while she holds the line.
- Spend reactions to deny. Shell Wall is her best tool, use it to harden herself or the boss she guards, and punish the attacker with cold damage on a miss.
- When bloodied, dig in harder. Moon-Tide Vigil gives +2 AC and Con saves while she stays put, so a bloodied Sentinel that refuses to move only gets tougher to crack.
- Three ways to run her: doorway gatekeeper in front of a boss; a pair of them sealing both ends of a corridor; or a lone vigil over a glyph-stone the party must reach and stand on.
Cancer
Medium monstrosity, lawful neutral
CR 6 · 2,300 XP · GUIDELINECarapace Sidestep. The Sentinel can move sideways at full speed and ignores difficult terrain. Opportunity attacks against her are made with disadvantage while she moves.
Moon-Tide Vigil. Signature. So long as the Sentinel holds her ground and does not willingly leave a 10-foot space, she gains a +2 bonus to AC and to Constitution saving throws as the zodiac tide steadies her. The bonus is lost the instant she moves more than 5 feet from that space, returning on the start of any turn she ends adjacent to it again.
Actions
Multiattack. The Sentinel makes two Pincer attacks. If both hit the same target, the target is grappled (escape DC 15).
Pincer. Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit: 14 (2d8+4) slashing damage.
Brine Lance. Ranged Spell Attack: +7 to hit, range 60 ft., one target. Hit: 16 (3d8+3) cold damage, and the target's speed is reduced by 10 ft. until the end of its next turn.
Bonus Actions & Reactions
Shell Wall (Reaction). When the Sentinel or a creature she can see within 5 feet is hit by an attack, she interposes a claw, granting +3 to that creature's AC against the triggering attack. If this causes the attack to miss, the attacker takes 7 (2d6) cold damage.
A crab-plated guardian fused with her own carapace, she sits in eternal vigil before a glyph-carved obelisk, two great chitinous claws curving up from the dais like the horns of the summer constellation. She does not hunt; she holds.
Cancer, Bound
Companion · acts on your initiative
Bound · GUIDELINEAnchored Ward (signature). While within 10 feet of the creature it has sworn to guard, Cancer grants that creature a +1 bonus to AC and cannot be moved against its will by any effect that does not also move its ward.
Actions
Snapping Claw. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 9 (2d4+4) bludgeoning damage, and the target is grappled (escape DC 13) if Cancer has a free claw.
Reactions
Take the Blow. When its ward within 5 feet is hit by an attack, Cancer makes itself the target instead, taking the damage in their place.
A lesser crab-thing of the Colony, bound to a single charge, it scuttles a tight circle and lets nothing reach the one it has sworn to keep.
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.
Plant her in a doorway or on a stair and let the party come to her, since she fights at her best when she never moves. Open with Brine Lance to slow a runner, then pincer-grapple the first melee fighter to lock them in place. Kill-priority is anyone trying to drag her off her spot; pair her with a flagship boss she is sworn to protect.
Set her as the immovable gatekeeper: she holds the chokepoint while a bigger threat works behind her. Open by grappling the strongest melee PC with both pincers, then spend reactions on Shell Wall to keep herself or the boss alive. If clustered, she is fine eating an AoE because Moon-Tide Vigil and her resistances soak it; the real way to beat her is to force her off her square. She is the anchor piece, not the centerpiece, pair her with a flagship.
Run her as a stationary wall in front of a higher-tier boss, where her grapple and Shell Wall trivialize a single attacker. Open by locking down the party's mobile striker, then defend the boss with reactions every round. Kill-priority is forced movement and grapple-breaking, those are the only fast answers; otherwise she stalls the fight indefinitely.
Put Cancer 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 Cancer?
Her home stat block is CR 6 (2,300 XP), tuned for a party of levels 5-10. She is an add-on anchor rather than a solo boss, so she has no legendary actions; scaled-down (CR 2) and scaled-up (CR 11) versions are provided in the tier table.
Can Cancer be a companion or ally?
Yes. As a lawful guardian she makes a fitting bound sentinel for a vow-keeping paladin, an oathbound order, or anyone defending a threshold. The included companion, Tidewatch, Bound, is a lesser crab-thing that shields a single charge and can stand in as her own escort.
Why is she a monstrosity and not a celestial?
Though her sign hangs among the stars, the render is plainly a crab-fused warrior of flesh and chitin, not a radiant outsider, so monstrosity is the truest SRD fit. Frame her through the public-domain myth of Karkinos, the crab set in the heavens as the constellation Cancer.
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
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