On to the hydroloth, toadlike denizens of the River Styx that presumably show up from time to time in the water features of the material world. They’re technically Amphibious, able to breathe both water and air, but they have very little reason ever to want to come out of the water, because that’s where all their advantages lie.
Hydroloths have an unusual ability contour: extraordinary Dexterity (first) and Intelligence (second), with very high Constitution coming in third. What to make of this? It seems like first and foremost they’re designed for fast melee assault, since they don’t have any ranged weapon attack that could take advantage of that Dex. Secondarily, they rely on magic, in the form of Innate Spellcasting and Steal Memory. Finally, if they need to tank it out for a bit, they have the Constitution to do that; they prefer to settle a fight quickly and decisively, but they’ll settle for an attrition battle if they must. They’re extremely good at assessing the specific weaknesses of their opponents—good enough to read stats off a character sheet—but with a Wisdom of only 10, they tend to be indiscriminate in their target selection and slow to figure out when they’re outmatched.
Hydroloths are immune to acid and poison and resistant to cold, lightning and physical damage from normal weapons. They’re vulnerable to fire, but whether they avoid it or go berserk in its presence will require more analysis. Like dhergoloths and merrenoloths, they have overlapping darkvision and blindsight, making darkness (which they can cast at will) particularly advantageous for them, without the usual problem of being unable to see through it oneself. They have Magic Resistance, and therefore no particular fear of spellcasters, and they’re immune to the memory-wiping effects of the Styx, as well as to mind-reading.
They have an unusual and interesting Multiattack that gives them a choice between two melee attacks (Bite/Bite does marginally more damage than Bite/Claws or Claws/Claws, so unless they’ve invented a magic item that provides resistance to piercing damage but not slashing damage, I can’t think of a reason not to choose Bite/Bite) and one melee attack plus a spell. The latter option is appealing, given that we’re looking at a creature that’s probably a hybrid of melee fighter and spellcaster, but to exceed the opportunity cost, the spell has to offer something more than a second Bite attack would. What are the choices?
- Control water is especially potent if the hydroloth’s enemies are adjacent to water rather than in it: by raising the waterline with the Flood option, the hydroloth can turn a large area into its own preferred turf. The Part Water and Whirlpool options are useful in other circumstances, but when it comes to storming the beach, Flood is the hydroloth’s jam. A caveat: Because it requires concentration, the hydroloth can’t have control water going at the same time as darkness. (This is going to be a recurring theme.)
- Crown of madness compels an opponent to switch sides and deal damage on the hydroloth’s behalf. However, an opponent with a Wisdom saving throw modifier greater than +1 has too good a chance of succeeding on the initial save, and an opponent with a Wisdom save mod of +1 or +0 has a decent chance of shaking it off in round 2. Also, the hydroloth has to use its own actions to maintain control of the charmed opponent, so this isn’t adding anything to its action economy; if anything, it’s detracting from it. Why do it, then? A couple of possibilities: Crown of madness has very long range—120 feet—and therefore allows a hydroloth to deal melee damage indirectly without being anywhere near the fight. Not a bad way to soften one’s enemies up before engaging oneself. Also, if the charmed target is capable of dealing more damage in one turn than the hydroloth is—unlikely, but possible—using its action to force the opponent to attack is better for the hydroloth than using its action to make attacks of its own. Like control water, crown of madness requires concentration to sustain.
- Fear requires concentration as well, and it drives opponents away when the hydroloth probably wants to keep them around to make melee attacks against them. But it does have one magnificently dirty application: It causes its targets to drop what they’re holding if they fail their saves. If the hydroloth is being attacked by a foe with a magic weapon—which deals full damage to it—casting fear has a chance of making the foe drop it. And if combat is taking place in the water, the dropped magic weapon doesn’t just clatter to the ground: it sinks into the depths, whence the hydroloth can go fetch it later, when it’s convenient. Against two or more opponents in the area of effect who are wielding magic weapons, this application alone makes fear quite appealing. (It also suggests that any PC willing and able to dive for a hydroloth’s loot stash should find at least a couple of nice magic weapons in it.)
- Phantasmal killer is a trap option. A spell save DC of 16 isn’t high enough to nullify the two fundamental flaws of this spell, which are (a) that it does no damage the first round it’s in effect, merely imposes the frightened condition, and (b) that just one successful saving throw shuts it down. The damage the spell deals on a failed save—4d10, or an average of 22—doesn’t arrive until the round after it’s cast, and only if the target fails two saves in a row. For a target to have at least a two-thirds chance of failing a DC 16 Intelligence save twice in succession, it would have to have an Intelligence saving throw modifier of −2 or worse. Granted, if you have a −2 or worse Int save mod, the hydroloth knows it, and if you have a −1 or better, it knows that, too; it’s not going to blow this opportunity on the wrong target. But for you, the Dungeon Master, the easiest course of action is simply to rule this spell out and never think about it again.
- Suggestion has its uses, most of which lie outside the boundaries of a combat encounter—at least, a combat encounter with a hydroloth. With most creatures, the suggestion will have to be made telepathically. And, again, it requires concentration.
- Darkness is very powerful for the hydroloth, which can cast it at will. Because it has blindsight, darkness imposes no penalty at all on the hydroloth’s attacks and in fact gives it advantage on attacks against any target who doesn’t have some ability to penetrate the magical blackout, while imposing disadvantage on those targets’ own attacks. This is good anytime, but it’s especially good anytime a hydroloth finds itself in the unpleasant circumstance of having to fight on land. It’s less spectacular underwater, where the hydroloth already has advantage on all its attacks, but giving your opponents disadvantage is still better than not giving them disadvantage. If it’s casting darkness as part of a Multiattack, the hydroloth will cast the spell first, then attack its blinded target.
- Detect magic requires concentration and is better cast before combat than during. Just assume that the hydroloth has cast it already as routine reconnaissance and knows what kind of juju the PCs are packing.
- Dispel magic does not require concentration, making it a spell that the hydroloth can cast flexibly whenever it needs to, whatever else it’s doing; the hydroloth can also cast it at will. “Any spell of 3rd level or lower on the target ends.” Water breathing is a 3rd-level spell. Who feels like drowning today? There are any number of other excellent buff spells that a hydroloth might want to snuff out (haste, enlarge/reduce, invisibility, protection from evil and good, magic weapon), but water breathing is at the top of the heap.
- Invisibility, which requires concentration, is somewhat redundant to darkness: both have the effect of concealing the hydroloth from foes it can see, giving it advantage on attacks against them and giving them disadvantage on attacks against it. Moreover, invisibility terminates as soon as the hydroloth casts a spell or makes an attack; darkness doesn’t. So why cast invisibility instead? Well, a commonly observed problem with darkness is that, unless it’s filling an entire enclosed space, targets can simply walk out of it, provided they know which direction to go. Also, unless it’s cast on a moving or movable object, its area of effect is stationary; invisibility goes wherever the hydroloth goes. So I’d say whether to cast darkness or invisibility is mainly a function of three things: How confined is the battlespace (darkness the more confined it is, invisibility the less confined it is), is the hydroloth’s posture aggressive (darkness) or defensive (invisibility), and does it need the effect to last (darkness) or not (invisibility)?
- Water walk seems at first to be more dead weight. Why does a hydroloth want to hop around on top of water when it has advantage on attack rolls while submerged in water? But the hydroloth doesn’t cast water walk on itself. It gives this ability to allied creatures so that they don’t suffer memory erasure from falling into the Styx. For the right price, it might even sell this service to player characters.
In addition to its spells, the hydroloth has two non-attack actions: Teleport (60-foot range, otherwise self-explanatory) and Steal Memory. Steal Memory is the unique and interesting one. Usable only once a day, and therefore only against one opponent, it inflicts 4d6 psychic damage and potentially wipes its memory, taking away all its proficiencies, spells and capacity to communicate. This is the closest thing the hydroloth has to a ranged attack. 4d6 sounds like quite a bit of damage, but it’s not, really: on average, it comes out to 14, no better than a simple Claws attack. The other stuff is what matters.
The thing is, the hydroloth isn’t a particularly disciplined creature, and as I mentioned before, it’s indiscriminate about its target selection—mostly. Once again, we’re looking at a save DC of 16, which is decent but not outstanding. Against a target with a +1 or lower Intelligence save modifier, it can be expected to work at least two-thirds of the time. Against a target with a better save mod, it starts to look like a waste of an action.
I resolve the matter thusly: The hydroloth uses Steal Memory against whoever has the poorest chances of resisting it. That much, it can tell. It has no other criteria. It doesn’t say, “Oh, it would be really useful to take this person out of the fight for reasons x, y and z; I should give Steal Memory a shot against them.” Nah, it just looks around, sizes its opponents up, decides whether any of them seems mediocre in the IQ department, and hits ’em with it. If there is no good target, then it probably won’t bother.
Taken together, these features and traits form an incoherent package. To make sense of it, we have to figure out what the hydroloth’s priorities are. Is stealing memories the main goal or just a means to an end? The flavor text offers a clue, suggesting that hydroloths aren’t independent agents at all—that they have masters that they serve, and that they deliver the stolen memories to those masters. But it also suggests that they contract out to attack ships or seaside settlements. So I think we need to begin with the premise that they have two main jobs, each with a different modus operandi. Possibly three main jobs, actually, since attacking a ship and attacking a fishing village are tasks that call for different approaches.
If the job is to steal memories, the hydroloth’s abilities make it almost unfairly easy. Using invisibility to approach within 60 feet of a promising target, the hydroloth uses its Steal Memory action against them . . . then leaves. Steal Memory technically isn’t an attack or a spell, so using this feature doesn’t break the hydroloth’s invisibility. The target is left with a splitting headache, a mere fraction of their former brainpower (if they fail their saving throw) and no explanation. The hydroloth doesn’t even need to fight if its target’s allies don’t immediately start scouring the area for it. We can’t even call this a combat encounter, really: it’s a MacGuffin, a hook that sends the party off on a quest for answers and a cure.
A hydroloth attacking a ship can’t try to demolish the ship directly, the way, say, a kraken can, but it can attack the ship indirectly, by using control water to Part Water or create a Whirlpool underneath it. Part Water is an extremely dirty trick: First, it causes the ship to fall to the bottom of the trench, where it topples over on its side because it can’t balance on its keel. Once that’s happened, the hydroloth can simply drop the spell and let the water pouring into the trench fill the ship up so that it no longer floats. (Does the descent deal falling damage to the ship and everyone on it? I’d say no: The water beneath the ship parts; it doesn’t vanish. As the water parts, the ship slides down into the part, rapidly but not so rapidly that it would result in free fall. Both ship and crew might take falling damage from the ship’s subsequent toppling, but that would amount to only about 20 feet’s worth.) If you feel like this stunt is too unsporting, you can use the Whirlpool option instead and deal 2d8 bludgeoning damage per round to the ship’s hull. That’s not going to make much of a dent in a 300 hp sailing ship, though. The Flood option doesn’t work against most ships: they’re too large to be capsized by the wave.
Aside from making players’ jaws drop, the chief advantage of the Part Water maneuver is that it forces all the hydroloth’s opponents into the water, where it has Watery Advantage, a 40-foot swimming speed (compared with the 15-foot speed that most humanoid opponents will have) and no need to either hold its breath or employ magic to avoid drowning.
Before it does any of this, however, the hydroloth approaches the ship under cover of invisibility, situates itself directly underneath, then switches to detect magic to do a sweep for magic weapons, buff spells and other arcane effects of note. When that’s done, it switches back to invisibility (gotta love those at-will Innate Spellcasting spells!), moves 40 feet away from the ship, then switches to control water to open the trench.
Once the hydroloth’s enemies are in the drink with it, the real hostilities commence. Normally, it just zeroes in on the most isolated enemy within movement range and Bites twice. But there are a few exceptions: If its sweep revealed one or more magic weapons, it follows a path that will let it cast fear (area of effect: 30-foot cone) on those wielding them, in an attempt to make them drop them; it does this as the first part of its Multiattack, then closes to melee distance and Bites as the second part. If the sweep revealed a troublesome buff on the enemy it’s going after, it casts dispel magic first, then closes to melee distance and Bites. If at least three of its enemies are all within 15 feet of a central point, it casts darkness to envelop them, then closes and Bites. And if at least two enemies who’ve managed to hold onto their magic weapons engage it in melee, it Bites first, then casts invisibility and slips away from them; on its next turn, if those enemies have Wisdom saving throw modifiers of +3 or lower, it tries fear on them again, and if they don’t, it pursues an easier target. It uses Steal Memory if and only if it has a suitable target in range and can’t reach any melee opponent.
Fighting on land differs from fighting in the water in a couple of ways. First, the hydroloth doesn’t bother to come ashore to reconnoiter for magic stuff, because the fear stunt doesn’t have the same effect as it does in deep water. Instead, it leads with control water, immediately Flooding the shore. Second, it can’t use invisibility, darkness, fear or crown of madness while fighting onshore, because all these spells would require it to drop concentration on control water. Now, if its concentration on control water is broken, that’s another matter. A beached hydroloth summons another Flood if it can, but once it’s out of uses of control water, it casts darkness or invisibility instead. If it’s using darkness, it casts the spell as the first part of its Multiattack so that it can gain advantage on its attack roll in the second. If it’s using invisibility, it attacks first and casts the spell second, so that it can remain unseen between turns. While fighting, it tries to keep its back to the open water, not because it means to flee that way but to try to bait its opponents into following it there. If they do, it can try to trap them there with a control water Whirlpool (if it has any use of that spell left).
In fact, a hydroloth anywhere other than Gehenna, Hades or the Styx itself doesn’t flee at all—it knows its essence will re-form if its physical vessel is destroyed. But like other yugoloths, a hydroloth can be killed on its home turf, and if it’s seriously wounded (reduced to 54 hp or fewer) in one of these locations, it Teleports as far away from its enemies as it can, then swims away at top speed.
Next: flail snails. Sorry, I just need a break from yugoloths for a bit.