## It levels the playing field

Casting darkness will cancel out both advantage and disadvantage, due to the way they stack.

If your opponent has advantage and you have disadvantage, then cancelling both will be good for you, and bad for them.

## It benefits those who can see through magical darkness

Some characters (eg, Warlocks with Devil's Sight) can see normally in magical darkness.

So, their opponent will be blinded, but they won't.

I want to start out mentioning the *Cloak of Displacement*. It's **supposed** to mess with sneak attack. Going back several editions, it's done a great job of it. Even thematically, it's very hard to attack a vital point when you effectively have double vision against the target (likely more like multidimensional double vision, but I digress). I don't think you need a way to "fix" that the character couldn't have snuck-attack.

With that said, we're currently utilizing this house rule in a game I'm playing, so....

### Generally, it doesn't affect overall game balance

In my opinion, it's less fun, because it's more bean-counting. It very much reminds me of editions from years past where you frantically tried to add various numbers together in order to get to the magic number you needed.

*"Okay, I rolled a 7, plus my 6 to hit. That's 13. Wait and I have the plus 2 from charging and another plus 1 because this is my favorite weapon. That's 16. OH OH OH Bardic inspiration! 17!"*

Maybe you liked that, but I did not.

In most cases, it's a moot point because you only have one source of advantage and disadvantage anyway. In the rare case that it actually matters and you get to apply [dis]advantage in a case where you couldn't not have otherwise, it's no more or less exciting than any other scenario where you would normally get to apply [dis]advantage.

If this is something you're thinking of instituting at your table, talk it over with the players and come to a consensus. Remember that D&D is, by and large, a bad reality simulator and should not be viewed with too fine a lens, lest you see the frayed threads within.

## Best Answer

The numbers in the DMG result from calculating the probability of a hit and then seeing how many attacks are needed to produce one hit on average. For example if a creature needs to roll 17 to hit, it has a 20% chance or 1 in 5. So if 5 creatures attack 1 will hit in average. If you make the same calculations with advantage (rounding 1/chance to hit) you get this scale:

$$\begin{array}{c|c|} \text{d20 roll needed} & \text{Attackers per hit} \\ \hline \ 1-10 & 1 \\ \hline \ 11-16 & 2 \\ \hline \ 17 & 3 \\ \hline \ 18 & 4 \\ \hline \ 19 & 5 \\ \hline \ 20 & 10 \\ \hline \end{array}$$

With Disadvantage:

$$\begin{array}{c|c|} \text{d20 roll needed} & \text{Attackers per hit} \\ \hline \ 1-3 & 1 \\ \hline \ 4-8 & 2 \\ \hline \ 9-10 & 3 \\ \hline \ 11 & 4 \\ \hline \ 12 & 5 \\ \hline \ 13 & 6 \\ \hline \ 14 & 8 \\ \hline \ 15 & 11 \\ \hline \ 16 & 16 \\ \hline \ 17 & 25 \\ \hline \ 18 & 44 \\ \hline \ 19 & 100 \\ \hline \ 20 & 400 \\ \hline \end{array}$$

If you compare this with +5/-5 you will see that it the case of Advantage the flat bonus would be much more [ehem] advantageous for mobs with a low chance of hitting. Needing a 20 would become needing a 15. The DMG would then give a hit per 4 attackers where the full calculation shows you would need 10. Also if you apply -5 for Disadvantage, a mob that needs 16 or more to hit would have zero chance. This is not really a practical concern as 16 or more enemies can rarely surround a PC, but still a theoretical difference.