What balance pitfalls result from this house rule regarding the Incapacitated condition?

Question

For an upcoming campaign I'm considering a set of hacks to give 5e a more visceral sense of danger. One such hack would eliminate the incapacitated condition altogether and use stunned in its place. If it isn't obvious, the goal would be to heighten the vulnerability of a combatant rendered incapable of acting. What game-balance pitfalls would likely result from such a rule?

To elaborate: incapacitated is already subsumed within stunned, so the only balance issues I foresee would involve game elements that impose the incapacitated condition without also imposing stunned. For example, hypnotic pattern imposes incapacitated but not stunned, and as a relatively low-level spell, it conceivably might cause problems for low-level parties. Then again, hypnotic pattern is arguably overpowered already. Granting advantage to land a single hit on a target affected by hypnotic pattern probably won't worsen that problem much; at most, it'll just hasten an encounter hijacked by hypnotic pattern to its conclusion a bit faster.

Surely, however, I'm missing something. What am I missing? Pitfalls involving fiends would be of special concern, as the campaign will include Descent into Avernus.

(Note: I'm not interested in frame-challenge answers. I know there are other games that do this or that better than D&D. I routinely advise people who propose hacking D&D to make it more this or less that that they might be better off just finding a different game. In the grand tradition of not following one's own advice, I'm considering this house rule anyway.)

Answer 1

There are some things to consider:

Prevalance of condition immunity

Stunned has quite a few monsters immune. Incapacitated has none. That initially makes monsters immune to the condition that normally wouldn't be.

No means of ending the incapacitated condition

There are some (very limited!) means of ending Stunned

Makes things more dangerous

The incapacitated condition can be delivered via a lot of other means and conditions. Wrapping that into stunned adds additional negatives besides action restrictions.

Giving attacks advantage and autofailing strength or dex saves increases damage/death risk. You have also removed movement as an option by moving to Stunned.

This sounds like what you're going for, but thought I'd spell it out :)

Answer 2

Practical impact of these changes:

• Incapacitated has an additional effect of "attacks against this character gain advantage" and "Creature autofails Strength and Dex saving throws."

• Unconscious, petrified, and paralyzed have no change. They all had those features already.

Simple Incapacitated without any riders isn't an amazingly common effect. Tasha's Hideous Laughter inflicts it, as does Hypnotic Pattern, and Symbol(pain). Wind Walk inflicts it as a side effect while you're transforming back. Myconids have a certain spore attack that incapacitates and poisons. Torpor Poison (ingested) applies Incapacitated and Poisoned. That's... maybe about it? Basically, it's mostly unusual stuff and edge cases. If you think that Hypnotic Pattern is overpowered, this will make it worse. Other than that, it's just not that big a deal.

The rules pretty clearly intend that Incapacitated means "you can move defensively, but not offensively". If you can't do either, that's what stunned or paralyzed is for, and it makes a degree of sense for the sorts of effects mentioned that you might not be able to make a meaningful attack against the enemy, but might still be able to get out of the way of an attack.

I can see the feel that you're trying to go for, and that's fine. If just having the rule is going to have that kind of an impact, then it could be well worth it, but it really doesn't do much, because it's not going to come up much, because you almost never wind up incapacitated without also having one of the other effects that cover what Stunned covers. If you don't put in an effort to throw a bunch of Myconids at the party, then there's a good chance that the most common usage is going to be the PCs using slightly upgraded spells and/or poison to murderblender more effectively, and making Hypnotic Pattern even stronger than it already is.