He becomes unseen and unheard of, and his location becomes unknown as it loose track of it in the swirling snow. It just blinked out of it's radar if you prefer.
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I didn't say chameleon, i said camouflage, the art of blending in the surrounding. It's a Dexterity check because Dexterity is the attribute for moving nimbly and quietly to escape notice among other things.
The Dex check is simply an action resolution mechanism that is used not to find out if you followed through on your declaration to stay quiet, etc., but to see how successful those efforts are in keeping your location secret. As Crawford says, it's a requirement of the hide-attempt rather than the attempt itself, which is a fictional action rather than a game mechanic.
I've juxtaposed these two quotes because they hone in on the issue that I'm most interested in.
Here's the ingame situation I have in mind: it is snowing; a wood elf is standing in the snow, being observed by a human (let's say they're even conversing); and then the player of the wood elf (be that player or GM) declares "I am going to try and hide from the human."
Is that action declaration permissible per se? Does it automatically fail, because the elf is under observation?
My sense of this discussion is that Plaguescarred, [MENTION=23751]Maxperson[/MENTION], [MENTION=6857506]Harzel[/MENTION], [MENTION=413]Uller[/MENTION], and probably one or two others I've left out, thing the answer is "Yes, it is permissible per se; and does not automatically fail, and permits the player of the elf to make a DEX check to remain unseen and unheard."
My question is - what happens, in the ficion, to constitute the attempt to hide? The human can already see the elf through the snow - what changes so that the human can no longer do this? Does the snow get heavier? Does it suddenly blow into the human's face, briefly blinding him/her? It's all very well to say that the elf "blinks out of the radar", but how? Why? What has happened, in the fiction, to bring this result about?
Plaguescarred, if you think the answer is
camouflage, what is happening in the fiction at the moment the action is declared, such that the non-camouflaged elf suddenly becomes camouflaged? (The reason I thought of chameleon-like camouflage is because that seemed the most obvious answer I could think of.)
Can the elf, in effect, use a supernatural ability at will while in the snow?
I'm still a little unclear on the situation. Was the templar NPC merely invisible, or was s/he making some effort to hide? Also, were there any other PCs present, or just the one that was the target of the psionic attack? I don't know about 4e, but 5e makes it clear (as I'm sure you know) that an invisible creature's location is known until it begins trying to hide
4e's Stealth rules are almost identical to 5e's hiding rules (or maybe, given the sequence of authorship, I should state that the other way around) - the only significant differences are that 4e's rules are stated slightly more formally in terms of their interaction with the cover/concealment/LoS rules, and it also has more formal rules for the difficulty imposed on the DEX check by moving. In 4e, as in 5e, if you attack a target whose location you are guessing but don't know, you take a penalty to the attack (-5 in 4e, rather than 5e's disadvantage).
In the scenario I'm describing, the templar was (from memory) around 20 feet away from the PC in question; stood up (to negate an attack penalty); used the psionic effect that creates the invisibility to that foe; and then attempted to hide (in the sense of being still and quiet). The opposed rolls were made, and the templar won, and hence - by the rules - became hidden, unable to be seen or heard by the PC and with his/her location unkown.
The templar's position was suspected, though - I don't think any other PC was telling the targetted PC where the templar was, but area where the conflict was occurring was a square surrounded by buildings, and the PC was standing in the nearest exit (between two building). And the PC can also be fairly confident that, if the templar moved, it wasn't very far (in the fiction, because the character didn't notice any footsteps, dust etc; mechanically, this is expressed by the fact that moving more than 10' imposes a -5 or worse penalty on the DEX check, and the PC has a high bonus for Perception and so the player can be confident that anyone who beat the check probably wasn't taking movement penalties).
I think the slight awkwardness of the situation (as I felt it, at least) was the contrast between the relative certainty that the templar must be in the same place where he stood up, with the "official" situation that his location was unknown to the PC. As I think about it, I think this tension has the following cause: in the fiction, the PC continues to believe - intellectually, if you like - that the templar hasn't moved, but suddenly lacks perceptual access to this truth; whereas, at the table, the players' understanding of the situation is purely intellectual, because they are not actually in a dusty square between building looking at a templar. So the player of the PC doesn't experience the same contrast, and sudden lack of perceptual information, that the PC does: the player continues to have the intellectual belief about the location of the templar, and is simply contrasting this with another intellectual belief that the PC can no longer perceive that location.
As I reflect on it, I'm thinking more about how I need to work on my narration of this sort of situation (it could well come up again, given the prevelance of psionics in Dark Sun). I can't substitute perceptual for intellectual beliefs, but can try and make it clearer what has happened to the PC (emphasising the sudden loss of perceptual access to the templar's location), and avoid using more intellectual-type language (like "You don't know where the templar is") which tends to produce the slight dissonance I've tried to describe above (because the player really does know where the templar is, or at least has a pretty good idea of it).
I hope the above makes the situation a bit clearer.
