Sea spawn are humanoids who once lived normal lives but in one way or another have been “lost to the sea”—either by violating some maritime taboo or by falling under the sway of some powerful underwater denizen. Because they can survive out of the water for no more than a day, their transformation dooms them to live the remainder of their lives beneath the waves.
With an ability contour that peaks in Strength and Constitution, sea spawn are straightforward, and fairly uncomplicated, melee fighters. However, since their Piscine Anatomy allows three variations, you can enliven a sea spawn encounter by throwing a mix of types at your player characters.
Sea spawn have 30 feet of swimming movement vs. 20 feet of normal land movement, a strong incentive for them to fight in water (where they can move twice as fast as a typical humanoid foe) rather than out of it (where they’re 33 percent slower). Similarly, their 120 feet of darkvision is a strong incentive for them to attack only at night or in water so deep that sunlight doesn’t penetrate.
A sea spawn’s Multiattack consists of two Unarmed Strikes plus one Piscine Anatomy attack, which can be a Bite, Poison Quills or a Tentacle. Bite does straight piercing damage, and not very much of it. Poison Quills deal poison damage—even less of it—and also have a chance of inflicting the poisoned condition on the sea spawn’s target. But the poisoned condition only offers indirect benefit to the sea spawn: its target suffers disadvantage on attack rolls and ability checks, but the sea spawn itself doesn’t gain advantage, so the only result is that the target has a harder time fighting back. Also, the saving throw’s DC isn’t hard to beat; unless they’ve dumped Constitution, nearly any low-level PC will succeed on their save at least 50 percent of the time.
Tentacle not only deals the most damage, albeit not by much, but also is the only option of the tree that offers an actual tactical wrinkle. Since it has a 10-foot reach, a sea spawn can engage its target from that distance, and if its attack hits, the target is grappled, meaning it can’t come any closer to the sea spawn and therefore may not be able to fight back. Inconveniently, however, this longer reach doesn’t apply to the sea spawn’s Unarmed Strike. Consequently, if it remains at this distance, it has to forfeit two-thirds of its Multiattack.
Can the sea spawn at least make a judgment call about when it’s better to remain at tentacle’s length from its foe vs. when it’s better to close in and pummel? Not with Intelligence 6, it can’t. It has one approach to combat and mechanistically follows that approach whether it’s working or not. Nor does it have the Wisdom to judge which of its targets needs most to be grappled. Therefore, we have to assume that it fights the same way as its fellows, moving in close enough to use all its attacks. However, let’s give it the benefit of the doubt about one thing: When its opponent tries to run away, rather than strike back immediately with an Unarmed Strike, this sea spawn variant waits for it to try to move more than 10 feet away, then lashes out with a Tentacle and tries to stop it in its tracks. Since Tentacle deals an average of 5.5 damage on a hit, vs. Unarmed Strike’s 4.5, this is a smarter move anyway—even if the target succeeds on its saving throw and eludes the grapple (again, not hard to do).
Plus, sea spawn can have a combination of Piscine Anatomy traits and choose which one to use on any given turn. Thus, a sea spawn might choose to use Poison Quills most of the time during combat but switch to Tentacle when a foe retreats, or it might choose Poison Quills when its opponent is poisoned and Tentacle the rest of the time. (This last heuristic may be a bit too sophisticated for a standard Intelligence 6 sea spawn, though. Maybe save it for an “elite” sea spawn that’s a cut above the rest.)
Based on their origins, one might reasonably argue that sea spawn would have little self-preservation instinct and would fight to the death, but I think their Wisdom 10 indicates otherwise. However, there’s nothing to suggest that they’re unusually attached to their lives, either, so we’ll stick with the usual criterion of serious injury (12 hp or fewer) for deciding to flee. They’re not smart or disciplined enough to Disengage, and with their low Armor Class, Dodging doesn’t provide enough benefit, so they Dash away, diving back into the water at the earliest opportunity if they’re not already in it.
Next: shadow mastiffs.