Deepfin
Beast -- Huge -- Open coastal water, deep inland lakes, flooded valley systems
It surfaced once, about two hundred yards off the port side, and we had time to understand what we were looking at before it went down again. That was twelve years ago. I have made the crossing fourteen times since. I have seen three more. They do not come near the boat. I do not know what that means. I have stopped asking the question because I do not think the question has a useful answer.
-- master's log, deep-water crossing vessel, coastal transit service
Ecology
The Deepfin is the apex aquatic predator in open deep water: a huge, fast, echolocating cetacean-lineage animal that has been in the interior lake and coastal systems long enough to have developed significant adaptations to the variable Miasm conditions those environments produce. The Blindsight range -- 120 feet of echolocation-based spatial awareness -- gives it complete three-dimensional mapping of its environment in conditions where nothing else can sense anything. In deep, turbid, or lightless water, the Deepfin is not operating with reduced information. It is operating with more information than most things around it have.
They are not aggressive toward surface traffic under normal conditions. The behavioral record -- drawn largely from crossing-vessel logs over a long period -- consistently shows Deepfins approaching vessels out of apparent curiosity, maintaining distance, and departing. Attacks on surface vessels are documented but rare, and the documented cases cluster around specific triggers: sustained water disturbance near calving grounds, the acoustic signature of distressed large prey, and -- in several documented cases -- the Miasm disruption produced by active psionic channeling at or near the water surface. A Deepfin that has associated psionic channeling with the acoustic signature of distressed prey may respond to channeling the way it would respond to a food signal.
The social structure is small-group: three to six individuals, with cooperative hunting behavior observed in open-water scenarios against large prey. Cooperative hunts involve coordinated approach from multiple vectors in a pattern that disrupts prey escape routes -- the same spatial awareness that makes each animal a formidable individual predator makes the group a coherent tactical unit.
The thirty-minute breath-hold is a documented physiological fact, not an estimate. Individuals have been tracked descending to depths that place them below light penetration for extended periods. What they find there is not known.
Stat block
| AC | HP | Speed | Initiative |
|---|---|---|---|
| 12 | 90 (12d12 + 12) | 5 ft., Swim 60 ft. | +2 (12) |
| STR | DEX | CON | INT | WIS | CHA |
|---|---|---|---|---|---|
| 19 (+4) | 14 (+2) | 13 (+1) | 3 (-4) | 12 (+1) | 7 (-2) |
Skills Perception +3, Stealth +4
Senses Blindsight 120 ft.; Passive Perception 13
Languages None
CR 3 (XP 700; PB +2)
The Deepfin can hold its breath for 30 minutes. Melee Attack Roll: +6, reach 5 ft. Hit: 21 (5d6 + 4) Piercing damage.Hold Breath
Bite
Encounter use
Deepfin encounters are most effective as pressure rather than direct combat -- a huge animal with 120-foot Blindsight in its own medium, moving at 60 feet per round, is not something most parties want to fight in open water. The encounter is about the crossing: something this large is nearby, it is aware of the party, and the party needs to decide how to behave. Use the psionic-channeling trigger to create a meaningful constraint for Mages, Sages, Bloodborn, and any other channeler in the group -- active channeling in deep water near a Deepfin is a specific and documentable risk. A party that crosses without triggering the animal's threat responses completes an encounter without violence; a party that fights in its medium against CR 3 with Huge HP and 5d6+4 bite damage learns something about environment selection.
Salvage
Deepfin are large enough that a coastal settlement with the equipment to process one has food and material for weeks. The blubber layer provides both fuel and waterproofing compound. The acoustic tissue of the melon -- the fatty structure that focuses the echolocation signal -- is of significant interest to Lattice researchers working on passive sonar and deep-water sensor arrays; a fresh melon in good condition commands a high price from any research collective with underwater infrastructure. The bone structure, particularly the jaw, is dense and strong enough for structural applications where weight is not a constraint.