2024 Dwarven Stonecunning & Tremorsense rulings together.

Quote from RWinnie >>

Unless Tarod shows up with an official SAC or something, RAW would imply that a dwarf could only activate stonecunning while on stone, but once activated, it would function like normal tremorsense so long as the dwarf remained in contact with a stone surface. Tremorsense, meanwhile, defines what a "surface" is in its own description - the ground, a wall, or the ceiling. So, if you are a dwarf, and you are standing on a boulder in the middle of the river, you could pinpoint the location of any other creature in contact with the ground within sixty feet of you. If there is a catfish feeding off the algae in the muddy riverbed within sixty feet of you, you would be able to pinpoint its location. If there was a person standing on the sandy shore fifty feet away, you could pinpoint their location. If there was a salmon swimming through the river, you could not sense it, as it is not touching the ground.

If you, the dwarf, jumped into the river, you would not be able to sense anything, because your stonecunning would crap out the moment you weren't touching the boulder. However, if you were to reach out and grab hold of the boulder, you would be able to sense the catfish, the person on the shore, and the salmon in the water, because now, you are in contact with a stone surface and touching both the same surface as the catfish and the guy on the shore and the same liquid as the salmon.

Likewise, if you were standing on the stone floor of a castle, and there was a fountain full of fish in the castle, you could pinpoint the location of the catfish on the bottom of the fountain, but not the Koi swimming through the water unless you walked into the fountain. You also wouldn't be able to pinpoint the location of the Giant Spider on the wall or the Roper hanging from the ceiling. But if you touched the wall, you could sense the Giant Spider, and if you could somehow also touch the ceiling, you could sense the Roper. So, if you were standing in the worst-designed castle on earth, where you could stand in the fountain while touching the wall and the ceiling, you could pinpoint the location of every creature I just listed. You could not, however, pinpoint the location of the flumph floating in the air behind you. 

If you want to argue that these rulings are inappropriate, I agree that the water thing is probably something I wouldn't allow regardless of RAW, but that's how the rules are written.

You are going to have to better explain your logic about the water. The interior of water is not a surface, so anything swimming in it is not in contact with a surface you are also in contact with. At best, the surface of the water could be used to detect things that are also on the surface of the water. As I said before, if you allow for detecting things inside the water that you are also in, then you should be allowing for detecting things in air that you are also in. There is no difference.

I will concede, however, that the rules taken together seem to say that a stone surface merely "activates" Tremorsense in dwarves. I don't like it. I don't think it is what they were going for in terms of the fantasy. And I don't think I would rule it that way in my games. But it does appear to be what the text says.

Quote from RWinnie >>

Unless Tarod shows up with an official SAC or something, RAW would imply that a dwarf could only activate stonecunning while on stone, but once activated, it would function like normal tremorsense so long as the dwarf remained in contact with a stone surface.

 The way i read it, for 10 minutes a Dwarf on a stone surface with Stonecunning's Tremorsense activated can pinpoint the location of creatures and moving objects within a range of 60 feet, provided that the Dwarf and anything it is detecting are both in contact with the same stone surface.

If during this time the Dwarf go swimming in a lake for example, it can't use this Tremorsense to pinpoint anything because it is not on a stone surface, this has been my ruling ever since based on the article The 10 Species in the 2024 Player's Handbook | Dungeons & Dragons

Stonecunning: The 2014 features have been replaced. You now can gain Tremorsense for 10 minutes on stone surfaces as a Bonus Action. You can use trait a number of times equal to your Proficiency Bonus.

And that 100% clarifies intent. It, unfortunately, doesn't rewrite the rules that are written, though.

Quote from sabin76>>

You are going to have to better explain your logic about the water. The interior of water is not a surface, so anything swimming in it is not in contact with a surface you are also in contact with. At best, the surface of the water could be used to detect things that are also on the surface of the water. As I said before, if you allow for detecting things inside the water that you are also in, then you should be allowing for detecting things in air that you are also in. There is no difference.

I will concede, however, that the rules taken together seem to say that a stone surface merely "activates" Tremorsense in dwarves. I don't like it. I don't think it is what they were going for in terms of the fantasy. And I don't think I would rule it that way in my games. But it does appear to be what the text says.

 Tremorsense's description specifically says: "Tremorsense can pinpoint the location of creatures and moving objects within a specific range, provided that the creature with Tremorsense and anything it is detecting are both in contact with... the same liquid.*"

So if you have Tremorsense, and you are in contact with a body of water, you can sense anything else in contact with that body of water. In fact, if the aforementioned Flumph is dipping a tentacle into the water to get a drink, you can pinpoint its location, even if it is floating in the air.

Also, the rules specifically say: "As a Bonus Action, you gain Tremorsense with a range of 60 feet for 10 minutes. You must be on a stone surface or touching a stone surface to use this Tremorsense."So you can actually activate Stonecunning to get Tremorsense while you're floating in thin air. Stonecunning will be active for 10 minutes that whole time. However, you cannot use the Tremorsense unless you are on or touching a stone surface, but that also means that you can use the Tremorsense anytime you are on or touching a stone surface.

Now, again, I accept that the intent of the rule might be that you can only sense things that are on the same stone surface as you while you are on a stone surface, but the rules as written clarify that you simply need to be in contact with any stone surface (defined as a floor, wall, or ceiling) in order to gain the full benefits of Tremorsense.

* The OP added the "only stone for Dwarven Stonecunning" line, and it is not in the actual description of Tremorsense.

Quote from RWinnie >>

Unless Tarod shows up with an official SAC or something [...]

 I wish I had something, but the official intent was already provided, and I think it's a very good answer and ruling.

Quote from RWinnie >>

Quote from sabin76>>

You are going to have to better explain your logic about the water. The interior of water is not a surface, so anything swimming in it is not in contact with a surface you are also in contact with. At best, the surface of the water could be used to detect things that are also on the surface of the water. As I said before, if you allow for detecting things inside the water that you are also in, then you should be allowing for detecting things in air that you are also in. There is no difference.

I will concede, however, that the rules taken together seem to say that a stone surface merely "activates" Tremorsense in dwarves. I don't like it. I don't think it is what they were going for in terms of the fantasy. And I don't think I would rule it that way in my games. But it does appear to be what the text says.

 Tremorsense's description specifically says: "Tremorsense can pinpoint the location of creatures and moving objects within a specific range, provided that the creature with Tremorsense and anything it is detecting are both in contact with... the same liquid.*"

So if you have Tremorsense, and you are in contact with a body of water, you can sense anything else in contact with that body of water. In fact, if the aforementioned Flumph is dipping a tentacle into the water to get a drink, you can pinpoint its location, even if it is floating in the air.

Also, the rules specifically say: "As a Bonus Action, you gain Tremorsense with a range of 60 feet for 10 minutes. You must be on a stone surface or touching a stone surface to use this Tremorsense."So you can actually activate Stonecunning to get Tremorsense while you're floating in thin air. Stonecunning will be active for 10 minutes that whole time. However, you cannot use the Tremorsense unless you are on or touching a stone surface, but that also means that you can use the Tremorsense anytime you are on or touching a stone surface.

Now, again, I accept that the intent of the rule might be that you can only sense things that are on the same stone surface as you while you are on a stone surface, but the rules as written clarify that you simply need to be in contact with any stone surface (defined as a floor, wall, or ceiling) in order to gain the full benefits of Tremorsense.

* The OP added the "only stone for Dwarven Stonecunning" line, and it is not in the actual description of Tremorsense.

Holy crap... skipped right over that last part. Apologies.

Then, I fully agree that your ruling is RAW. However, I think Plaguescarred's edit including the article leaves absolutely no room to interpret intent any other way. "You can use Tremorsense on stone surfaces" is not "you can use Tremorsense while on stone surfaces" or "you can use Tremorsense while touching stone surfaces". Those latter two would be closer to allowing general tremorsense by carrying a stone amulet or something like that. But intent as written in the article is quite clearly meant to limit tremorsense itself to stone surfaces.