D&D 5E 5E underwater thoughts

[Bitbrain]

The secondary DM for my group once had an entire session of his homebrewed campaign take place underwater.

He ruled that fire would deal only half damage, and that thunder would deal maximum damage (to the great delight of the Thinderwave-spamming Bard)

 

[Tony Vargas]

Spells? How do I address the fact that water and fire, lightning and cold just don't mix? Yeah, I could handwaive it as "it's magical" but I really don't want to. Are there good alternatives?

The same general tricks that worked back in the day should work now. Fire just doesn't work underwater, cold has a reduced range/area and might create a nice big chunk of ice in the area, lightning changes from whatever it shape it was supposed to be into a burst.

Playable races? I'm not a particular fan of either monstrous races or "underwater humans with blue skin"

There's water genasi, I suppose. You could have a race of Atlantean/Lemurian style humans who don't breathe water or have blue skin, but do have skills & equipment adapted to living underwater, either magical or fantasy-tech type solutions - like the scuba gear made from giant shells in the old Mysterious Island, for instance.

and I'm particularly lost as to what would be good underwater variants of gnomes and halflings. Sure, I could leave them out, but I'd like to have something.

There are sea elves, so I suppose you could have sea-gnomes, who are also fey. If you use the 3e-gypsy-style halflings, they could be wandering in ships instead of caravans; if you use the traditional hobbitsy-borrowing halflings they could live in comfortably-renovated air-filled gaint-monster-shells, like communal hermit crabs.

Radiant: I mean, it's light, right? So will water diffuse it in some way?

Murky water perhaps enough so to make a difference, sure.

Cold: Will a cold spell freeze water? Could a ray of frost even travel underwater?

Yes & yes. Shorter ranges & smaller areas, but leaving ice behind. Could be interesting/different.

Poison: Would Poison Spray be diluted underwater?

Yes, then again, it becomes an 'inhaled' toxin, since it'd be absorbed by the water-breathers in the area.

Acid: Or Acid Arrow?

Acid would presumably be 'washed off,' too, though, it might be deadly by damaging gills.

Thunder: Water is a better conductor of sound than air, so would that affect spells like Thunderwave?

Seems reasonable. It might create an actual wave.

I once had a DM who kept getting caught up on the science of how things should work, and pretty soon we were having to deal with convection and the "crushing depths of the sea floor", among other things.

It's a valid style, and one D&D has certainly tended towards in some ways at some points.

But, so is ignoring science and psuedo-science implications and just letting fantasy be fantasy. Factoids like "you can't get enough air breathing through a straw to remain conscious" or details like the specific heat of water or whatever can be safely ignored.

 

[Sunseeker]

The secondary DM for my group once had an entire session of his homebrewed campaign take place underwater.

He ruled that fire would deal only half damage, and that thunder would deal maximum damage (to the great delight of the Thinderwave-spamming Bard)

Hmmm, I like that, seems like a fair compromise, some magic gets buffed, some magic gets nerfed.

So here's what I've got so far:

Bludgeoning weapons always attack with disadvantage.
Ranged weapons auto-miss any target out of range. No bows. Crossbows are now Spearguns.
Fire deals half damage (this effect is applied to the fire, not the submerged creatures as 5E currently rules).
Thunder always deals max damage, but has friendly fire.
Lightning deals an additional 1/2 damage 5ft out in all directions from it's origin and has friendly fire.
Cold deals half damage and has a chance (what % seems reasonable? I'm thinking 10%) to form a solid block in the affected area.

 

[77IM]

When you flash-freeze water, particularly salty water, you can get a "slush" effect. So I'd have freezing spells create difficult and obscuring terrain in their area. If the area was already slush, then it freezes solid.

I like fire dealing half damage. That's an excellent compromise between "it doesn't work, because physics" and "it works just fine, because magic."

 

[77IM]

I like the idea of thunder spells having increased range. I think making them deal max damage may be overpowered if the entire campaign is under water. In fact if the entire campaign is underwater you might want to adjust spell levels. Maybe fire spells are 1 level lower and thunder spells (if you keep the max damage) are 1 level higher.

In fact, if the campaign is entirely underwater, you could go the opposite route: keep all the spells the same as what it says in the PHB. But for those rare occasions when the party is fighting in AIR, then fire spells deal double damage, thunder spells deal half damage, etc. This will be MUCH easier than adjusting most spells every time you cast them.

 

[mrpopstar]

Throw a fireball underwater, and you get a larger stream of bubbles, which then explodes, creating a concussion under the waves, as well as an area of not just boiling water, but rolling boiling water, effectively flash cooking everything in a 20 radius SPHERE. Not a circle, but a sphere, because now you are dealing with 3 dimensions, not two.

You are always dealing with three dimensions, not two, when throwing a fireball.

Each creature in a 20-foot-radius sphere is affected, not a 20-foot-radius circle.

 

[Tony Vargas]

You are always dealing with three dimensions, not two, when throwing a fireball.

Nod, but under water just about anyone can swim in three dimensions, even if not very well - unlike flying through the air.

On land you aren't 'always' dealing with 3 dimensions, for instance, if no one in the party flies, only battles where at least one enemy does will automatically go '3D' - especially if the battlefields tend to be comparatively level.

 

[Sunseeker]

I like the idea of thunder spells having increased range. I think making them deal max damage may be overpowered if the entire campaign is under water. In fact if the entire campaign is underwater you might want to adjust spell levels. Maybe fire spells are 1 level lower and thunder spells (if you keep the max damage) are 1 level higher.

In fact, if the campaign is entirely underwater, you could go the opposite route: keep all the spells the same as what it says in the PHB. But for those rare occasions when the party is fighting in AIR, then fire spells deal double damage, thunder spells deal half damage, etc. This will be MUCH easier than adjusting most spells every time you cast them.

I think that, for as much as I want to keep things simple, I want that constant reminder that you are underwater and things don't quite work the same. If I only changed things for the occasional surface fight, I think I'd lose some of the mechanical reinforcement of "Yes, you are under water." The catch to thunder under water is I think the friendly fire, affecting even the caster.

Nod, but under water just about anyone can swim in three dimensions, even if not very well - unlike flying through the air.

Right, though I think the flying sniper is much less effective, since your enemies can "fly" and everything past about 60ft (I think that's the Heavy Crossbow range) auto-misses.

 

[mrpopstar]

Nod, but under water just about anyone can swim in three dimensions, even if not very well - unlike flying through the air.

On land you aren't 'always' dealing with 3 dimensions, for instance, if no one in the party flies, only battles where at least one enemy does will automatically go '3D' - especially if the battlefields tend to be comparatively level.

This is true.

 

[Yaarel]

The 6th-level spell Freezing Sphere is cold damage that explicitly freezes water into ice.

Inferrably, all lower level spells only great slush − not solid ice − thus difficult terrain that obscures vision.