Balance implications of removing unseen-attacker advantage when mutually unseen

Question

The rules for unseen attackers (PHB p. 194-195) specify that attacking a creature that cannot see you = advantage, and attacking a creature you cannot see = disadvantage:

When you attack a target that you can't see, you have disadvantage on the attack roll. This is true whether you're guessing the target's location or you're targeting a creature you can hear but not see. If the target isn't in the location you targeted, you automatically miss, but the GM typically just says that the attack missed, not whether you guessed the target's location correctly.

When a creature can't see you, you have advantage on attack rolls against it. If you are hidden–both unseen and unheard–when you make an attack, you give away your location when the attack hits or misses.

This creates some arguably counterintuitive situations when neither party in a conflict can see each other, like two warriors fighting each other in a pitch-black room hit each other exactly as much as they would in broad daylight, or archers whose vision of their targets is entirely blocked shoot with as much accuracy as if they could see their targets perfectly.

As a result, I am considering making the following modification (in bold) to the second rule in my game:

When a creature can't see you, and you can see it, you have advantage on attack rolls against it.

This would mean that being unable to see your target gives you disadvantage regardless of whether they can see you or not, instead of the disadvantage and the advantage cancelling themselves out.

What impact might this have on game balance, in terms of feature interactions or anything else? Does this change cause any major balance shifts?

Answer 1

Overall, reasonably well-balanced

Fog cloud will work how people think it works

I can't tell you how many times I have seen people suggest using fog cloud as cover against enemy archers. Even Treantmonk lists it as a benefit of the spell in his popular guide to 5e wizards. With your proposed change, it will actually work as expected in this and other cases. Particularly-bizarre cases are also fixed. RAW, you are far more likely to hit a target 600' away with a longbow if you (or they) are obscured by fog.

Higher AC creatures benefit more

Your proposed change inflicts disadvantage on attacks by most creatures within fog cloud or darkness. The higher a creature's AC, the better this change is for them. The following examples illustrate this. (Critical hits are ignored for now.)

• An AC 16 wizard is hit 50% of the time by an orc with +5 to hit. With disadvantage, the wizard is hit 25% of the time. Disadvantage caused them to take 50% less damage.
• An AC 21 fighter is hit 25% of the time by an orc with +5 to hit. With disadvantage, the fighter is hit 6% of the time. Disadvantage caused them to take 76% less damage.

Furthermore, a larger percentage of the hits on a high AC character are crits, compared to a low AC character. With disadvantage, crits happen 1 out of 400 times instead of 1 out of 20. This benefits high AC characters more than low AC ones.

In my experience, PCs - except those in the back line - tend to have higher AC than their opponents. A first level fighter with the Defense fighting style can have AC 19, rising to AC 21 once they get plate. Thus, the PCs will usually benefit more from the changes than their enemies.

Sneak Attack is worse

RAW, you can Sneak Attack someone in a fog using only the adjacent ally rules. Now, you'll also need to hide or get Help to cancel the disadvantage.

Advantage-generation is better

Various spells, Reckless Attack, and the Help action are better with more disadvantage in the mix. Since PCs tend to hit more than they miss, it is usually better to cancel disadvantage than it is to gain advantage.

Wind wall gets slightly weaker

Wind wall is only really useful when defending or assaulting a fixed position, where your own ranged attack capabilities are much less than the enemies'. You may be able to peek out from the side of the wall, shoot, and then take cover behind it again.

With the proposed changes, fog cloud is a reasonable substitute. At 3rd level, it provides a whopping 60' radius of fog, covering your approach for around the same distance as wind wall - 120'. Fog cloud only provides disadvantage on ranged attacks, while wind wall causes them to miss entirely. On the other hand, fog cloud also blocks almost every non-AoE spell cast by most creatures.

Warding wind is largely unchanged

Warding wind only affects those around you, so your allied archers and casters can still hit foes that aren't engaged with you. It also hedges out fog, which may become more prevalent with your proposed changes. These differences help it maintain its niche.

Conclusion

Tanky PCs will want fog cloud to make them more evasive. Control casters won't want it, since it blocks their view. Wind wall and warding wind will continue to have niche use cases. Using the term "realistic" to argue about D&D 5e is a losing battle, but the proposed changes add a degree of verisimilitude and tactical depth without disrupting the overall balance.

Answer 2

This won't affect game balance, but it will make combat twice as long and half as fun

From the start, these rules only interact this way when both sides are mutually hindered. The change doesn't affect who can see in the obscured area, so interactions where 1 side can perceive the other are unchanged.

The only change will be giving obscured combatants on both sides disadvantage, which will roughly affect all hit chances equally. This will mean, in situations where a character would have missed, they still miss, and where they would have hit, they might miss. This will just drag combat out without making any meaningful difference. If 2 characters stand in the dark and wale on each other statistically the same one will win as before, they'll just do it after taking a lot more time.

There is more to being unseen than advantage

While the game mechanics make it seem like shooting an arrow at someone you can't see (and who can't see you) is just as likely to hit as if it where in the middle of a large field, the reality is that you miss outright if you don't target the correct location. If you can't see your opponent you literally can't target them, you need to guess which square they are in. If you can tell where they are via sound or some other sense then you have a chance to hit, but otherwise if you choose the wrong square there is no hope in hitting them.

Also remember that tohit rolls and AC are the game's way of abstracting combat down, they represent the constant dodging, parrying, and weaving that characters do in the midst of combat, and having the advantage/disadvantage cancel each other out shows that, not only is the attacker shooting blindly, but the defender can't see it coming to attempt to dodge, for example.

Answer 3

It would favor spellcasters.

Your modification only affects attack rolls.

It is the only form of attack available to most NPCs, as well as fighters, rogues, monks, barbarians... They will hit less often, and inflict overall less damage.

Spellcasters, on the other hand, have many options to harm opponents without having to rely on attack rolls - some of which don't even need vision. If you know the opponent's approximate position, thunderwave and fireball still inflict the same damage.

Moreover, spellcasters have means to create obscured areas, as an example through fog cloud or darkness. They may be tempted to use those spells more often.