D&D 5E Swimming and combat : rules clarification

[firstkyne]

This is a continuation of a discussion which granted on another thread. I would like to ask this question of 5e experts.

I have an idea for a scene. The area is flooded under 4 feet of water with some sections subject to fast flowing. I am trying to make sure I stay as close to the rules as possible, but I need more detail than provided. Here what I have so far.

It is Difficult Terrain: medium sized creatures move at half speed, small creatures must swim to move.

Creatures of up to medium size may swim, if they wish. While swimming, each foot of movement costs 1 extra foot, unless a creature has a swimming speed.

Areas of rough water, or where the flow is counter to a creature's direction of travel, require a successful Strength(Athletics) check.

Rough/counter flow: DC15. Failure: cannot move. Critical failure, creature is carried by the water 2d4 x 5ft.

Very rough/counter flow: DC20. Failure: creature is carried by the water. Critical failure, creature is carried by water 2d4 x 5ft and takes buffeting damage 1d6 (bludgeoning).

Rough water with rocks in: tbc

V rough water with rocks in: tbc

Combat under water

When making a melee weapon attack, a creature that doesn’t have a swimming speed (either natural or granted by magic) has disadvantage on the attack roll unless the weapon is a dagger, javelin, shortsword, spear, or trident.

A ranged weapon attack automatically misses a target beyond the weapon’s normal range. Even against a target within normal range, the attack roll has disadvantage unless the weapon is a crossbow, a net, or a weapon that is thrown like a javelin.

Spells in water

Any Lightning keyword attack hitting someone in water hits everyone in the water

Any lightning keyword attack fired by someone in the water hits everyone in the water instead of it's target

Any fire damage attack deals half damage

5 to save against ongoing fire damage

Attacking a submerged creature from above the surface: tbc

Drowning

Tbc

Can you help me fill the gaps?

 

[jodyjohnson]

1. By the rules there are no 'critical failures' for ability checks. The closest is usually a 'fail by 5 or more', in this case I'd go fail by 10 or more.

2. Checks you're expecting the whole party to need to make shouldn't be DC 20, or even DC 15 unless the group is higher level.

3. If your group is higher level they will bypass this with Flying, Water Walk (3rd level ritual) or some sort of rope use.

We just played through DDAL07-04 A Walk in the Park with a related scenario. It was a half hour of dice rolling. With the high DCs you are proposing the failure rate would be higher and it would take longer. Lots of 'nothing happens' rounds with no progress.

4. I'd do 2 categories but there needs to be an incentive to try crossing normally instead of avoiding it with magic. treasure in the water is a big incentive. Category 1: Rapid water DC10 - failure is just Quarter movement or swept downstream on fail by 5 or more. Cat 2 - Rapids with rocks, DC 13 or take 1d6 but still move 1/4 movement as the character use the rocks to keep from getting swept further.

5. Drowning is p.183 PHB (see Suffocating).

 

[77IM]

4 feet of water is a lot. Medium-sized creatures should have to swim. Swimming is already just as slow as difficult terrain, so it doesn't usually matter. But I'd say if a medium creature wanted to wade (for example, to keep a lit torch above water) they move at 1/4 speed, or "each foot you move uses up 3 additional feet of movement" in 5e language.

Creatures immersed in water are already resistant to fire damage so they already take half damage so you don't need to add that part.

The lightning thing is super powerful. I'd probably decrease lightning damage to compensate. Maybe lightning spells do half damage, but your saving throw is at disadvantage. I'd also have to think more on the radius of the lightning damage effect. At first glance 10 ft. radius per spell level seems fair. That's covering a lot of ground but at half damage. It does do something weird to spells like call lighting so maybe I'd halve the radius for spells with a duration.

There was a thread about this not too long ago. I think the other big discussion topic was thunder damage. Sound travels farther and faster under water. I'd probably double the area of thunder effects, but have them deal half damage, and disadvantage on saves. That's similar to the lightning thing but not exactly.

I agree with [MENTION=5590]jodyjohnson[/MENTION] about the swimming effects and DCs. Focus on having interesting consequences for failure, rather than making failure difficult. "DC 20 or you miss your turn" is super boring; "DC 10 or you are swept 10 feet and take 1d6 bludgeoning" is much more interesting.

 

[Satyrn]

Attacking a submerged creature from above the surface: tbc

I'd just make the attack roll at disadvantage, with spears and tridents getting to attack normally. Edit . . . Just realized what I quoted was about magic, not weapon attacks. Umm, I don't know. I'd probably just do things as normal, since it's magic.

I think you're over-complicating the rough water stuff. I don't think you need to distinguish between rough and very rough water. One category should be enough for your players to feel like they're in rough water, and it's less info that you have to explain.

Also, what you're calling rough water looks more like fast flowing water. While the "w/ rocks" thing your looking for help with is what I'd call rough water. Rapids are rough because of the rocks, after all.

And for fast flowing water, in combat, I'd require a DC 10 strength check to move any distance against the current, and at the end of a turn require another check to avoid being swept back at whatever speed I label the current (10 feet, probably).

For rough water, it's the same, but failing the check at the end of the turn would also inflict 1d6 damage for each 10 feet the character is forced to move.

Oh and a player moving with the current would get to move an additional distance equal to the current's speed (again, probably 10 feet). In rough water, maybe require a DC 10 Strength check to avoid taking damage while doing this.

 

[Caliban]

I generally treat shots through the Air/Water interface as granting the target 3/4 Cover (+5 AC, +5 to Dexterity saves), rather than Disadvantage.

If the target is submersed in murky water, then the attack would have Disadvantage (as you can't see them), but it may be canceled out if the target can't perceive you either.

Admittedly, this is based on how it was treated in 3e, but I feel it makes sense.

I'd also consider granting Resistance to damage from Bludgeoning and Slashing attacks, when that attack originates in or has to pass through at least a foot of water to reach the target. (It's really hard to generate or maintain momentum when swinging through water). Freedom of movement would negate this penalty.