Homebrew: Underwater Mechanics and 3D combat in Roll20 (D&D 5e)

"There is heroism and brute warfare on the ocean floor, unseen by land-dwellers. There are gods and catastrophes."
~ China Mieville, The Scar

That which lies below the waves is an interesting and terrible place indeed. It is also a great location for stories and campaigns, and as such saddens me that I cannot enjoy it more often. One of the primary reasons for this is due to the additional rulings, which are seen as limitations on characters that want to flex their entire skillset. Personally I am of the belief that these rules should not be seen as limitations, but as demonstrations of the pressures on aquatic life, and as a way to explore how these pressures have been overcome or coexisted alongside.

Below are some rulings that can be used by DMs that want to emphasise the effect of being in an aquatic environment on characters and objects. These rules would also be good to consider for subterranean games, as many underground rivers and sea caves and the like exist below the earth.

Core Rules

Official rules related to underwater gameplay can be found in the following areas:
Player's Handbook: breathing underwater/suffocation (pg 183); underwater combat (pg 198)
Dungeonmaster's Guide: extreme cold, frigid water, high altitude aka effects of pressure (pg 110); swimming (pg 116); underwater visibility (pg 117)
Ghosts of Saltmarsh: ocean environs (pg 202-207); currents, depth illumination (pg 203); pressure and objects (pg 204)

In addition, Appendix A of Ghosts of Saltmarsh includes rules on ships and naval combat; Storm King's Thunder also includes a ruling on damage at 3,000 feet below sea level (pg 203).

Demonata

In my childhood I was not always an active reader. That changed drastically around the time that I discovered the works of Darren Shan, an Irish author of horror novels. I got through each book of the Cirque du Freak series and each book of the Demonata series in a book-a-day layout, borderline devouring the pages upon finally finding something that really clicked with me. Throughout my time attempting (and failing) to write prose and as a tabletop game player, Shan's novels have definitively influenced both my creative works and me as a person.

It's therefore kind of a surprise to me that I haven't incorporated much of his worldbuilding into any games. Let's change that.

I'm going to preface this by saying that, as a primarily D&D player, I do not think this system is the best one for capturing the tone and feel of either the Demonata series or the Cirque du Freak series. D&D is a game of heroism, epic feats, and increasing in personal power. These do come into play in Shan's books as well, but rarely to the extent that D&D will give you. The characters are constantly against odds that cannot be fought head on, which eventually, inevitably, becomes the case in many D&D games.

There are ways to get around this- rule modifications, tone, level caps- but I would still recommend people consider other game systems for running games in Shan-inspired settings/tones. Perhaps I'll do a version of this post in a different game system as proof of this at a later time.

As the title of this post suggests, I'm going to focus on the Demonata series. The goal of this post is to outline some of the concepts within the series and then begin translating them mechanically into Dungeons and Dragons so players can use them for themselves. If people like where this goes, I'll add more to it, maybe do some stat blocks and stuff for it too.

Unsurprisingly, spoilers follow after the break.

Faction Prompt: The Stilyard

The Stilyard deal in luck, morality, and free will.

In return, you incur a debt to be paid. This is not a debt of coin, but a debt of choice. You owe them a moment of your free will.

You won't find them at city markets, nor do they have shops. The Stilyard keeps themselves hard to find, accessible only to those who truly have the drive to seek them out. Those that find them and those they seek out are a special clientele - individuals that live lives filled with harsh decisions, drastic action, and catastrophic failures.

Goals

The Stilyard's true objectives are hard to determine, but there are clues in their transactions. They trade free will for control, luck for finality, chaos for order. The Stilyard wants to see the world on a script, with each line pre-rehearsed and each part played correctly. Whilst it presents itself as a neutral party, it is an inherently Lawful Neutral faction, for the only payment it seeks is the ability to determine how events will play out. What exactly the final end point is is unknown, potentially even to the Stilyard themselves. But there is a degree of comfort in knowing where all the players in life's stage will fall, what their lines will be, and how things will end before the curtains fall.

Individuals that work for the Stilyard can apply to have their own choices and goals taken into consideration when payment is due - the degree of influence they have increases with the amount of dealings they make. In return, their power over decisions can only be used at the authorisation of the faction as a whole.

Cuombajj Witches by Seb McKinnon

Mechanics

Members of the Stilyard can provide two primary forms of service. Firstly, they can alter alignment (if such a mechanic exists in your game). Depending on the system, this may be a percentage/value reduction or a binary change, depending on whether the relevant mechanic is analogue or digital.

Secondly, they can sell luck. Mechanically speaking, they sell a predetermined dice roll to the player, which they can use to replace a roll of their choice, after which it is expended. For D&D 5e, this would allow them to replace an ability check, saving throw, or attack roll. Treat this as if the player is using the divination wizard's Portent ability.

In return, they seek control of a player's luck or free will in the future. For a dice roll, the Stilyard may choose the player to succeed or fail on a dice roll that would directly or indirectly benefit the Stilyard. The DM can either choose such a roll based on the action's consequences, or roll a d20 (or d100) and then determine that, in that number of rolls, the Stilyard makes its move. The roll the Stilyard chooses can either be proportional to the player's dice roll (e.g. a 1 for a 20, a 5 for a 15, a 3 for a 17 etc) or could be rolled immediately after the transaction is made.

For an alignment shift, the Stilyard requires a heavier price to be paid: 1d8 hours of a character's free will. There is no saving throw for this control.

d10	What the Stilyard does with your free will
1	You sign a devil's contract with your own blood
2	You march into a courtroom as a surprise witness
3	You set up an assassination for a passing noble
4	You tell a beloved friend the truth they needed to hear
5	You donate half your carried wealth to a noble cause
6	You deliver a package to someone in a back alley, then drink to forget
7	You allow a spirits to inhabit your body
8	You act as messenger for other Stilyard clients
9	You witness a brutal, unforgivable crime... and walk away.
10	Nothing seems to change from what you would normally do

Inspired by the Mann, Levinn, and Lewis Firm from Wildbow's Pact series.

Insight: Hard to Read

Your Wisdom (Insight) check decides whether you can determine the true intentions of a creature, such as when searching out a lie or predicting someone's next move. Doing so involves gleaning clues from body language, speech habits, and changes in mannerisms.

I like the Insight skill. It's one my characters use frequently, to gain that extra edge in social encounters. It is however no surprise that, despite the fact that I envisage its use like a Sherlock-scanner of intent and micro-expression analysis, it is used about 95% of the time to tell if a NPC is lying to me.

This is not just the case with my own usage - as the PHB itself states, Insight is used to tell if a creature is lying. This turns the Insight skill from a DM perspective into a binary response roll: the player detects a lie or does not detect a lie. However, the way in which a DM conveys this information opens up space to interpretation.

Consider the Rust Monster

Art from Dungeon of the Mad Mage, property of WotC

The origin of rust monsters is unknown, but multiple theories have arisen over time. The vast majority of these see these creatures as a form of curse or punishment on civilisation, degrading and feeding on the tools that separate them from wild beasts. Whether their creators are malicious and spiteful gods or malicious and spiteful mages is yet to be determined.

Rust monsters have slow metabolisms and are opportunistic feeders. The ravenous individuals located in dungeons are hungry and malnourished, having picked clean the iron and steel within, then gone into a state of hibernation until more food presents itself. Those found deeper underground, where metal deposits are easier to reach, are typically more docile than their overground counterparts. This does little to raise the spirits of the miners who have to deal with rust monsters feeding on the deposits they're trying to harvest.

If you find yourself traversing a dungeon with no locks on doors or bars on prison cells, be on your guard. Abandoned buildings from iron-age periods are a popular feeding ground for rust monsters. Villagers may inform you of a simple trick to avoid rust monsters: throw iron coins at them to distract the creatures as you flee. Do not do this. If you are curious to see why this is bad advice, try throwing some meat on the ground for a hungry dog and see if it will leave you alone afterwards.

Historian Guilds across the lands lament for the fragments of the past lost to their appetites. In regions where rust monsters were common, there is an increase in tool creation from non-ferrous materials; this also coincides with the amount of historic records present from bronze and brass age civilisations when compared to iron and steel age societies.

Amphipods make good visual references for rust monsters.
Photo by Katrine Kongshavn.

Regional variants of rust monsters possess different abilities. Some are mildly magnetic (advantage on attack rolls against targets in medium or heavy metal armour), with a few being so magnetically charged that weapons stick to their shells (akin to the kuo-toa's sticky shield trait). Others are more adapted to sneaking up on unsuspecting meals, with abilities such as standing leap or nimble escape. Some adventurers have reported finding cave-dwelling variants able to squeeze through narrow gaps and reach further than their cousins, allowing them to get at iron deposits deeper within the earth.

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The antennae of rust monsters can be made into weapons that possess similar properties, albeit for a limited period of time. They are especially favoured by thieves and saboteurs, as well as those frequently fight enemies in plate mail. Their limited longevity means that rust monsters must be harvested regularly in order to keep a ready supply; the severing of their antennae ensures the likely death of the creature, as it no longer is able to turn metals into rust, yet alone detect ferrous metals nearby.

Rust Blade/WhipWeapon (dagger or whip), uncommon 

This item is clearly made from the antennae of a rust monster, with a handle made of treated wood or bone. The weapon has the same properties as its mundane counterpart. If a target is wearing nonmagical metal armour on a successful hit, their armour class is reduced by -1. If it is reduced by -5, the armour is destroyed. If the attack roll is a natural 1, the rust blade or whip is broken and cannot be used as a weapon.
This item maintains its properties for 30 days. After this time has passed, the antennae loses its rusting ability and becomes brittle, disintegrating upon its next successful hit.

Attempts have been made to create Rust Armour, with the hopes of having the same weapon-degrading properties as the creature's exoskeleton. Attempts so far have been unsuccessful, with the plates flaking apart over time, as well as testers complaining about the fact that they are still injured each time the weapon makes contact with their armour.

Rust monster eggs can also be effective tools in warfare and sabotage. Individuals able to get them into an enemy's armoury or fortifications can cause the enemy to disintegrate from the inside out as the rust monster hatchlings chew through their weapon stores.

1d12 Dog Breeds

Feel free to change breed names; most of these are just stand-ins due to a lack of specific world locations.

1. Ghosthounds. Bred to sniff out ethereal undead. Seeking drive is triggered by the presence of ectoplasm. Sometimes trained alongside tracker dogs to find the source of the spirit's former body.
2. Shift Trackers. Bred to detect shapechangers. They rely on the scent of mimics and body snatchers to detect their targets, resulting in a culture of heavily perfumed doppelgangers.
3. Trollhounds. Bred to attack giants, trolls, orcs, and other brutish monsters. Large dogs, similar to Tibetan mastiffs. Variant breeds for hunting or fighting owlbears, yetis etc.
4. Mongrel Trollhounds. Named mongrels due to the experimental introduction of troll blood into their bloodline. Makes the resulting dogs tougher and gives them minor regenerative properties at the cost of hairlessness and unpredictable behaviour.
5. Familiar Friend. Small toy-dogs bred specifically to act as familiars. Smart and obedient, but heavily dependent on their owners for validation and company.
6. Droopy. A breed raised near Shadowfell breaches. Look like grey basset hounds - a common myth is that their skin sags because there's nothing under it but bones and sadness. Often crossbred with ghosthounds.
7. Steed-hounds. Gnomes and halflings have perfected the breeding of dogs as beasts of burden. These dogs are often docile to the point of tolerating almost anything, making them good family pets if they can continue to be put to work.
8. Pixie dogs. A small, furry breed kept as a companion. Believed by some to have the passive ability to charm those in their presence, resulting in them being treated more like children or idols than dogs.
9. Magicanine. Dogs that are exposed to magical energies at birth, resulting in shifts to their physiology. Treat as a regular dog with access to one or more of the following druidcraft, mage hand, prestidigitation, thaumaturgy.
10. False Magicanine. A regular dog painted different colours to look like a magical dog. Especially cunning conmen may use magic of their own to make the dog glow, levitate, breathe fire etc.
11. All Seeing Eye Dog. Can only see the future in greyscale.
12. Veteran-hound. A theraputic breed to help barbarians that wish to let go of their rage. Their senses are highly attunded to their masters' anxiety and tension, allowing them to comfort or distract them before the rage takes over.

For more dogs, check out this reddit post.

Arcane, Divine, Psionic

Magic in 5e D&D is divided into arcane and divine, with psionic being the figurative cousin twice-removed. I discussed this with two of my friends on the Discord of Many Things – ImFromNASA and tiredmoieties – and this is a rough take on the ideas we came up with for how scholars within a D&D world may interpret these three studies.

Magic is, at its most fundamental level, is the distortion of the natural state of things - the warping of reality. Traditionally we distinguish mages by where they take magic from: for example, druids take magic from the latent power of the natural world, whilst sorcerers are themselves producers of magical distortion.

The methods by which individuals seek to create distortion can also be categorised. These refer not to schools of magic, but instead schools of philosophy and ideology: states of viewing the world through which magic is magnified. The effect is similar to that of light refracted by different shaped lenses; the light – magic – is the same force, but the lens – an individual's philosophy – shapes how the magic emerges on the other side.

Premonitions of Chaos by Davide Ottoveggio

The most common of these mental states is that of Arcane magic. Arcanists view magic through the lens of trying to understand magic itself: breaking down the world into its fundamental components and learning how to reorder and reshape them. Spells, rituals, and incantations are all attempts at recalling the equations of creation. It is a form of magic that requires intense research and understanding of multiple fields of knowledge (unless of course you're a sorcerer who simply has an innate understanding of the way they may interact with the world, or a warlock who has such knowledge directly implanted into their minds).

Divine magic views magic through the lens of belief and faith. The individual views the world through a set of ideals and values, as well as through the pre-conceived notions of what their focus of faith (be it god, patron, ideal, or idol) is capable of. The individual then evokes this power, using their belief as the focus of magic. It is due to the nature of belief that clerics and the like can dip in and out of arcane power; as their faith wavers or is tempted, so too does their power. This also goes on to explain why different deity worship evokes different powers: the idea of what magic should do within a cleric's faith is just as influential as what magic theoretically can do.

Finally, there is the most elusive of magics: psionics. For many it is not considered true magic, due to the lack of material components or rituals. However, this is not due to the absence of magic, but instead due to how psionics is channeled. The Invisible Art is the inverse of Arcane magic: instead of focusing on known truths about the world, psionics focuses on the known truths of the self. It delves into one's own mind and notions of the world, using magic to then shape reality to fill in the gaps where reality doesn't quite match up. A psion's power is drawn from the understanding of the self and the self of others, allowing them to connect to the minds of others and free themselves from illusions designed to cloud the truths of their own senses from them.