Tidecrab
Beast -- Medium -- Coastal rock shelves, tidal channel margins, flooded lower-ruin levels, estuarine mud flats
It was not moving when we waded through and I did not see it until I was standing on it, which is when it saw me. It holds on. That is the part the descriptions leave out. The claw does not strike and release -- it locks and stays locked and you are pulling against something that has decided the situation is over and is waiting for you to agree. I got free. It cost me something. The guide said the large ones are in the deeper channels and I appreciated that she told me that after we were out of the water.
-- crossing account, lower tidal circuit
Ecology
The Tidecrab is a medium-bodied crustacean scavenger-opportunist that occupies the marginal spaces between water and solid ground. It is not a predator in the sense of tracking prey -- it is an opportunist that capitalizes on anything that comes within claw range, and in the tidal zones and flooded lower structures it inhabits, the density of foot traffic through its territory is high enough that "anything that comes within claw range" covers a significant range of encounter scenarios. The carapace provides meaningful protection; the claws are mechanical rather than venomous but apply the Grappled condition, and a Grappled creature in knee-deep water has additional problems the stat block does not fully capture.
They are not social in any organized sense, but tidal-zone populations cluster because the resources cluster -- the same mud flat or tide shelf that has enough detritus and small prey to support one Tidecrab will have a dozen in adjacent positions. The awareness of other individuals' feeding behavior means a successful strike by one animal will draw the attention of nearby crabs, not through coordination but through the same opportunistic response that governs all their behavior.
The Amphibious trait is ecologically significant: Tidecrab populations move freely between intertidal zones and open water and are the primary large invertebrate colonizers of flooded structures below the waterline. Lower levels of coastal ruin complexes are frequently Tidecrab territory. They do not pursue onto dry ground -- the exoskeleton desiccates in dry air more rapidly than the animal can manage -- but anything that crosses their floor is fair contact.
The nanite interaction is incidental and poorly understood. Tidecrab carapaces in high-Miasm coastal zones develop visible mineral deposits in the outer layer -- a kind of secondary calcification that appears to incorporate nanite-derived compounds. The practical effect is a marginally denser carapace in high-saturation populations, which the field record does not treat as a significant tactical variable but which researchers studying substrate-mineral cycling have found useful as a passive deposit indicator.
Stat block
| AC | HP | Speed | Initiative |
|---|---|---|---|
| 15 | 13 (3d8) | 30 ft., Swim 30 ft. | +1 (11) |
| STR | DEX | CON | INT | WIS | CHA |
|---|---|---|---|---|---|
| 13 (+1) | 13 (+1) | 11 (+0) | 1 (-5) | 9 (-1) | 3 (-4) |
Skills Stealth +3
Senses Blindsight 30 ft.; Passive Perception 9
Languages None
CR 1/8 (XP 25; PB +2)
The Tidecrab can breathe air and water. Melee Attack Roll: +3, reach 5 ft. Hit: 4 (1d6 + 1) Bludgeoning damage, and the target has the Grappled condition (escape DC 11). The Tidecrab has two claws, each of which can grapple one target.Amphibious
Claw
Encounter use
Tidecrabs are environmental hazards in flooded spaces, not combat encounters in open ground. The CR 1/8 is accurate for a dry-ground fight where the party has full mobility; it understates the problem in two feet of tidal water where a Grappled character cannot move efficiently and where five more crabs are two feet away. Use them to make flooded lower-ruin exploration a question of footing and attention: the party that moves carefully and checks where they are stepping encounters them as obstacles; the party that wades in fast finds out how the Grapple condition interacts with poor footing. Two claws per animal means one Tidecrab can occupy both hands of a grabbed target, and a cluster of three or four responding to the same disturbance signal can lock multiple characters simultaneously. They do not pursue out of the water.
Salvage
Tidecrabs are a reliable food source in coastal communities and the primary protein in the diet of settlements without access to land-animal herds. The shell material is durable enough for minor armor components and tool applications but not at the scale of larger creatures. In high-Miasm coastal populations, the secondary mineral layer on the carapace is occasionally refined for use in hardening compounds -- the nanite-derived deposits bond differently than standard calcium carbonate and have found niche applications in Lattice-adjacent materials work. The claws, separated and dried, are used as gripping tools in applications requiring non-slip mechanical contact.