Ok, so the article says pretty much the same thing Dungeon Craft does in his video on it; in fact the bullet point procedure in the video seems to have been taken directly from the article. Let me go through these points one by one.
• While describing the situation, the DM describes interesting features in the area.
This is just part of the basic play procedure as laid out in the How to Play section of the PHB, page 6 I believe. The DM should already be doing this all the time.
• The player describes how they want to use a feature to get a cinematic advantage.
Again, this is already part of the basic procedure of play, it’s just that in this case the specific thing the player wants to do is gain advantage on their next attack roll. But fundamentally, this is just the player’s part of the play loop, describing what they want to do and how.
• The DM determines what attribute and skill (or skills) might be used to accomplish the feat and how difficult it is on a scale of DC 10 to 20. Tell the player what the DC is and what penalty they face if they fail so they can make an informed choice.
And this, again, is just how the normal action resolution procedure should go. Slyflourish is assuming a possibility of success and failure and a consequence for failure all exist, but I don’t think that’s an unreasonable assumption to make in this context. What I will give Slyflourish credit for here though is codifying telling the player the DC and the consequence they’ll face on a failure. As far as I know, the 5e rules don’t explicitly instruct the DM to do this, but I do think it’s best practice.
• The player rolls the check as part of their move or action. On a success, they get advantage on their next attack. On a failure something bad happens depending on what they tried, often falling prone.
So, here we find the only part of this “new rule” that isn’t just restating the basic procedure of play. Specifically, allowing the player to take an improvised action as part of an attack (or the movement leading up to the attack) if the goal of the action is to gain advantage on the attack roll. And don’t get me wrong, I think that’s a good rule. I just don’t think it’s all that novel. Allowing certain tasks to be undertaken without using up your action in combat is a very common ruling. And I think this is a reasonable place to apply it.
Typically the results of failure are that you just can't do the thing you want to do.
I disagree. Generally an action needs a meaningful consequence for failure to be resolved with an ability check.
What slyflourish is outlining here is a game procedure, in particular while playing theater of the mind. He suggests offering environmental elements on index cards and actively negotiating with players as to how interacting with them would produce advantage and making clear the stakes of failure (which would likely be more than simply "you don't get to do the thing"). Then he offers 20 examples of what this might look like.
The index card thing seems like extra fiddly bits and bobs to distract from the action in the fiction, not to mention slowing down combat, and in my experience such things just lead to the players thinking of those index cards as buttons they can push to make something happen, instead of engaging organically with the fiction. I suppose, for some players this might be useful to break them out of only thinking about the options on their character sheet, but to me it seems unhelpful.
Crucially, he explains what this adds to your game if you are dm. We can compare with dmg p. 239 on advantage and disadvantage, which offers advice like
This is a suggestion, not a procedure. Further, it's vague: what's an example of "some aspect of the environment" or "exceptional" creativity or "circumstances"? It's nothing particularly profound, but I do find slyflourish writing to be more clear and more useful.
It’s meant to be up to the DM’s discretion what examples of such things might look like. Now, granted, the DMG is probably more vague than it should be in a lot of these cases, and I agree that Slyflourish makes a good case for what this adds to the game. My point was just that what he’s advocating for
is already part of the game, apart from the advice to let players improvise an action to gain advantage on an attack as part of the attack, and to use index cards to represent features of the environment (the latter of which I don’t even think is necessary for this “rule”).
Other examples would be the rules for tool proficiencies and downtime activities in Xanathar's. The writing there is more clear and the procedures and examples more detailed than what's found in the dmg.
I’m not a fan of the rules for these things in Xanathar’s. Tool proficiencies were already useful for adding proficiency bonus to ability check where they’re relevant, just like skills, and the DM could always grant advantage for tool proficiency at their discretion if they wanted that. The rules don’t really add anything there. Downtime they just straight-up made into uptime, which is fine I guess, but not what I want out of downtime rules.
The dmg just strikes me as a poorly written and organized book, even when compared to other 5e books, but especially when compared to dm advice from third party products or other games.
It’s definitely a poorly written and organized book, I agree with you there.